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Introduction to Software - Part 1

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Introduction to Software - Part 2



Introduction to Software

Software refers to the instructions placed in a computer’s memory to tell the computer what action to take. These instructions can be mathematical or logical. A group of instructions is referred to as a program, and a program loaded into a computer defines, step-by-step, what kind of a machine the computer will be.

When we load a check-balancing program, the computer helps us to balance the checkbook. Load a space-war program and the same computer becomes a space-war game. I will be showing interface programs you can use to communicate with your external hardware using C/MRI. These programs will include test software to make sure your system is operating correctly, as well as sample application programs.

The software examples presented in this C/MRI User’s Manual and in the Railroader’s C/MRI Applications Handbook are written with a primary emphasis of making them easy to understand and apply. After you have worked a little with the many examples provided, you will find that tailoring them to fit your specific railroad becomes a quite straightforward exercise.

Reading and writing program statements can be much like using the English language. For example:


It is straightforward to write and to understand: basically, if Block15 is occupied then Signal 24 is set to red. It would be difficult to make this any simpler. To handle the green case, for 2-aspect signaling, add the statement:


Alternatively, the red and green cases can be handled together using the statement:


This simply adds the “(or) else if Signal 24 is not red then it is green” statement to cover the situation when Block15 is clear. It presumes that if Block (15) is not occupied then it must be clear. Once you get the hang of it, understanding and writing such statements becomes a straightforward process and actually is fun to accomplish.

Feedback from hundreds of C/MRI user’s expresses such sentiments as: “I never dreamed programming could be such fun. Every time I add a few lines of code I have more functions running on the railroad. It’s great!”


Essentially independent of the details making up your C/MRI applications and also of the programming language used, you can be assured that most C/MRI programs will follow the fundamental format illustrated in Fig. 2-1.

Fig. 2-1. Software real-time loop – simplified

Each program starts by performing application initialization, such as defining the types of signals being used and the type of interface hardware connection implemented. Once this initialization is complete, the computer then enters a continuous loop to perform the following steps:

  1. Read inputs from the railroad
  2. Calculate railroad outputs based upon the inputs
  3. Write outputs to the railroad
  4. Go back to step 1

    This 4-step loop is repeated ad infinitum until you exit the program. It typically executes between 10 and 1000 times a second. At these speeds the computer software is essentially responding in real-time to events on the railroad. As an example, when the computer senses a train has crossed a signal block boundary, this results in the computer changing a signal to red. Because the computer software is forever rapidly repeating itself in a loop, while responding to real-time events on the railroad, the process is frequently referred to as a tight-infinite loop or as a real-time loop. In all that follows I will use the latter name.

    Example inputs in signaling applications include reading the status of block occupation detectors used to determine train position, turnout position to know what tracks are aligned, and control panel inputs such as may be found on a dispatcher panel. Example outputs include setting trackside signal aspects, aligning turnouts and setting display LEDs on control panels. The computer software uses the continuously updated inputs on each repetition, or iteration, of the loop, to re-calculate the changes in outputs and then it writes the updated outputs to the railroad.


    At this point I will focus on the logic portion of the program as illustrated by the central box in Fig. 2-1. It is the more creative part of programming. It is where we take the railroad’s inputs and decide, or calculate, what should be the corresponding outputs. How the inputs are read from the railroad and how the outputs are written to the railroad varies a little, based upon the interface hardware, e.g. SMINI, or SUSIC, so I will cover it later when we get more into hardware configurations. Examples of the logic we might need to program are:

    • Train approaching grade crossing so start flashers, bell and lower gates
    • Pushbutton pressed for yard Track 12 so align all switch motors for Track 12
    • Train just passed Signal 34E so set the signal to red
    • Block now clear so set signals leading into block to green
    • Dispatcher cleared traffic movement out of siding so align turnout for siding, then after a delay, set corresponding dwarf signal to green
    • Siding turnout now occupied so prevent it from being thrown
    • Train just passed dwarf signal so set it to red

    To begin to understand how easy it is to carry out such functions using C/MRI software, let’s look at a few examples.

    Signaling a Loop of Track

    Fig. 2-2 shows a loop of track divided into six signaled blocks labeled BK(1) through BK(6). Each block incorporates an occupation detector, such as a JLC provided OD or DCCOD, to inform the computer which blocks are occupied and which are clear. A signal is located at the end of each block and driven by the computer. The signal informs the train crew if the block ahead is occupied. I have labeled signals in the eastbound direction SE(1) through SE(6) and for the westbound direction SW(1) through SW(6).

    Fig. 2-2. Loop track with signals

    For this first example, I will start very simply by assuming 2-aspect, red and green, color light signaling. In later examples, and especially in the Railroader’s C/MRI Applications Handbook, I will look at much more complete and realistic signaling applications including implementing full ABS, APB, CTC and interlocking plants with all types of multi-aspect signaling. The C/MRI can do it all, more easily, more prototypically and at less cost than any other signaling method.

    However, we need to start someplace and I have chosen Fig. 2-2. Once we generate the logic for handling this simple signaling setup, it becomes a solid baseline from which to build more involved examples. Basically, we need to understand the basics before moving forward. There are many ways to program signal logic. At this point I will lead you through one approach to handle the signaling in Fig. 2-2.

    Most intermediate block signals on the prototype, like those in Fig. 2-2, display green unless the block immediately following the signal is occupied and then the signal is red. I will explain adding the yellow aspect a little later. At this point, to program the red-green situation, we will calculate the signal aspects using a two step process. First we will set every signal to red. At this stage, this initial red setting simply defines the signal aspect in the computer’s memory and does not directly affect the trackside setting. As a second step, we will look to see where blocks are clear and set the affected signals to green.  Once both steps are completed, we will write the signals to the railroad.

    Fig. 2-3 shows the program logic statements. For this example, I am defining a red aspect as RED and a green aspect as GRN. Also, the variable CLR is used to define a block as clear and OCC to define a block as occupied. The lines beginning with REM are remarks used to document or comment on the different sections of a program and they are not executed by the computer. I use them in all my programming to inform people reading the program of the purpose, or function, of the block of code that follows each REMark. Everything immediately following an apostrophe is also a remark.


            FOR I = 1 TO 6

                SE(I) = RED

                SW(I) = RED

            NEXT I


            IF BK(1) = CLR THEN SE(6) = GRN: SW(2) = GRN

            IF BK(2) = CLR THEN SE(1) = GRN: SW(3) = GRN

            IF BK(3) = CLR THEN SE(2) = GRN: SW(4) = GRN

            IF BK(4) = CLR THEN SE(3) = GRN: SW(5) = GRN

            IF BK(5) = CLR THEN SE(4) = GRN: SW(6) = GRN

            IF BK(6) = CLR THEN SE(5) = GRN: SW(1) = GRN

    Fig. 2-3. Signal logic programming for loop track

    I have elected to use a FOR-NEXT loop to initialize the 12 signals to red. The FOR I = 1 to 6 statement sets up a program loop where the first time through the loop variable I = 1, the next time through the loop I = 2, then 3, then 4 and so forth up to the last time through the loop where I = 6. The content of the loop is all statements between the FOR statement and the NEXT I statement. Thus, the first time through the loop, SE(1) and SW(1) are set to red. The second time through the loop SE(2) and SW(2) are set to red and so on up to the last time through the loop where SE(6) and SW(6) are set to red.

    Once the loop variable “I” reaches the value of 6, there is no NEXT I to increment so the program stops performing the loop and proceeds to execute the block of statements following the NEXT I statement. This next block of code simply looks at each signaled block and if clear it sets the affected signals to green. For example IF BK(1) is clear THEN SE(6) and SW(2) are set to green. However for the condition where Block1 is occupied, i.e., it is not clear, the statements after the THEN are skipped over keeping SE(6) and SW(2) at red.

    Once both blocks of code are executed, the program proceeds to write the outputs to the railroad and then to branch back to read in the detector inputs again and to recalculate the signal outputs. How the reads and writes are actually handled is covered in later chapters where are attention is devoted to specific node types, i.e. the SMINI and SUSIC.

    Approach Lighting Signals

    For another signal logic example, let’s assume a railroad has 50 signaled blocks and it is desired to implement approach lighting for all 100 signals. This means the two signals at each end of each block are dark unless the block in approach to the signals is occupied. Many prototypes do this to prolong bulb life, reduce battery drain during backup operations and now most importantly, to reduce vandalism. For this example, I have labeled the signal blocks with BK(I) and the corresponding signals exiting the block with SE(I) and SW(I) where the variable I, called a subscript because it is in parentheses, takes on the values 1 through 50.  To implement approach lighting for all 100 signals and the 50 blocks, we add the 6 program statements listed in Fig. 2-4.

          FOR I = 1 TO 50      

          IF BK(I) = CLR THEN

              SE(I) = DRK

              SW(I) = DRK

          END IF

       NEXT I

    Fig. 2-4. Programming approach lighted signals

    The FOR …NEXT statements set up a program loop, between the FOR and the NEXT that is executed 50 times. The first time through the loop the variable I = 1, the next time I = 2, then 3, 4, and so on up to 49 and finally 50. For each value of I, the IF THEN - END IF block of code is executed. For each signal block that is clear, the two statements that follow the IF are executed to set the signals at the east end and the west end of that block to dark. For each block that is occupied, i.e. not clear, the two statements setting the corresponding signals to dark are skipped over, keeping the signals at their previously calculated setting. Written in the form shown in Fig.2-4, the IF statement is referred to as a Block IF statement, which is used to head up a consecutive set of statements all relating to the Block IF condition. The END IF statement is always required to define the end of the Block IF set of statements. The following NEXT I statement defines the end of the FOR I = 1 TO 50 loop.

    Fig. 2-5 illustrates adding approach lighting to our previous loop of track. We simply copy the block of code from Fig. 2-4 and paste it at the end of Fig. 2-3. We then take the pasted code and change I = 1 TO 50 to read I = 1 TO 6. That is all there is to implementing approach lighting.

    It may seem inefficient that we first set all signals to red then we determine if a particular signal should be set to green and, if so, we set it to green. Then after we calculate the aspects for all the signals we go through them again and see if they should be set to dark. A key point is that we are only manipulating the signal aspect as it is stored in the computer’s memory. These internal-to-memory manipulations are having no immediate impact on the actual aspect of the trackside signal. It does not change until we have completed calculating all of our outputs, then transmitting them to the railroad via the interface.

    It is possible to include additional program branching statements and reduce the number of repeated times a given aspect may be calculated. For example, if a signal is going to be dark, skip the steps to determine what the aspect would be if it was not going to be dark.


            FOR I = 1 TO 6

                SE(I) = RED

                SW(I) = RED

            NEXT I


            IF BK(1) = CLR THEN SE(6) = GRN: SW(2) = GRN

            IF BK(2) = CLR THEN SE(1) = GRN: SW(3) = GRN

            IF BK(3) = CLR THEN SE(2) = GRN: SW(4) = GRN

            IF BK(4) = CLR THEN SE(3) = GRN: SW(5) = GRN

            IF BK(5) = CLR THEN SE(4) = GRN: SW(6) = GRN

            IF BK(6) = CLR THEN SE(5) = GRN: SW(1) = GRN



            FOR I = 1 TO 6

                 IF BK(I) = CLR THEN

                   SE(I) = DRK

                   SW(I) = DRK

                 END IF

            NEXT I

    Fig. 2-5. Programming loop track for approach lighting

    However, to take advantage of the computer’s super high processing speeds and to keep things simple it is best to proceed logically straight through every processing step each time through the real-time loop. This keeps programming simple, straightforward and easy to understand. These are the truly important precepts for effective C/MRI programming. Because our railroading applications are fairly low speed, maximum program efficiency and speed of computation are relatively unimportant.  For example, the total code in Fig. 2-5 probably executes in a fraction of a microsecond in today’s computers.

    Also, in general, IF-THEN branching takes longer than straight in-line calculations. My motto in all C/MRI programming is, “Keep your programming simple, straightforward and easy to understand!” Recalculating your signal aspects for several different conditions is typically much easier to understand than using a number of alternative and perhaps “nested” branching statements. The term “nesting” applies to where branching statements occur within other branching statements, which can lead to quite complex software behavior.

    Three-Aspect Signaling

    Let’s take another example and program the Automatic Block Signals (ABS) illustrated in Fig. 2-6 for 3-aspects, namely red, yellow and green. As before, the trackage is divided into signal blocks with an occupancy detector in each block. With ABS, and as we did in the previous example, a block signal is placed at the end of each block to inform the engineer if it is safe to proceed into the next block and if so under what conditions. Only eastbound signals are shown because westbound signals are handled in an identical manner. A train is placed in Block 5 to illustrate a typical set of aspects for the signals which are red immediately behind the train, then yellow, with the remainder of the signals being green.

    Blocks and signals can be identified anyway you desire and computer software can be written accordingly. To illustrate this point, in this example only, I will use complete names for the variables rather than the more typically used abbreviations. After this example I will change back to using the shorter, i.e. abbreviated, variable names, as they require fewer keystrokes for input and more information can be fitted on a given coding line.

    Fig. 2-6. Block signals used for ABS programming

    As before, every block and every signal needs to be numbered so they can be addressed individually by the software. We could use BLOCK1, BLOCK2, BLOCK3, etc. but it is often easier to use subscript notation, also referred to as an array. In programming these are written as BLOCK(1), BLOCK(2), BLOCK(3), etc. Although it is not mandatory, it is usually best to set up the numbering as 1, 2, 3, 4, etc. (i.e. starting with 1 and not skipping numbers).

    If you are not aware of it already, you will soon observe that programs can be written in many different ways using a multitude of different approaches and languages. The software programs included on the disk provided with this manual and the additional examples presented in the Railroader’s C/MRI Applications Handbook cover many railroad examples following all types of approaches and in several languages. For example, the handbook shows four different ways to program ABS signals. 

    This ABS programming example is set up to execute the block of statements in Fig. 2-7. It does this in a continuous loop many times a second. Therefore, as trains move from block to block, the signals change to reflect the correct aspects similarly to the prototype. To follow the prototype more exactly, we should calculate the aspect of Signal 5 ahead of Signal 4 and 4 ahead of 3 and so forth. This way each signal aspect calculation is using the latest available aspect of the other signals it needs for the calculation. You can arrange the blocks of code so that this is the case. However, at the high speed at which computers operate, the eventual results are identical. If a signal does have an incorrect aspect, such as red instead of yellow, it is corrected in the next iteration through the program, typically occurring a fraction of a second later.















    Fig. 2-7. Programming statements for ABS Signals 1 through 4

    Only two lines of code are required per signal. Use the same two lines for each signal on the railroad and simply change the subscript numbers. To save keying in every line, simply copy and paste the same block of code for as many signals as on the railroad and then go back and change the numbers. To see how the program works, we only need to look at Signal 1 as all the others function identically.

    The first line for Signal 1 simply reads – if Block 2 is occupied then set Signal 1 to red followed by a branch to calculate the next signal, which is Signal 2. That is pretty straightforward. If the computer finds that Block 2 is occupied and it sets Signal 1 to red there is no need to check out the other possible aspects for Signal 1. In essence, Signal 1 stays red no matter what else is true. If Block 2 is occupied, then we simply branch to process the next signal. The colon is used to separate the multiple statements placed on a given line.

    For the case when Block 2 is not occupied, the statements immediately to the right of THEN are skipped and we proceed with executing the second statement for Signal 1. This reads – if Signal 2 (the next signal down the line) is red then Signal 1 is yellow else Signal 1 is green. That’s about all there is to implementing signal logic for 3-color ABS signaling.

    Turnout Control

    Fig. 2-8 shows a track plan with five staging tracks converging down to a single track main. The same arrangement could represent tracks departing from a passenger terminal, or many other possible situations. Assume that each turnout is controlled by a Tortoise machine that is either wired directly to two C/MRI output pins or to a single C/MRI output pin via a JLC provided Switch Motor Control (SMC12) card. I will cover the actual wiring connections in the next chapter. One turnout control button is used per track, labeled 1, 3, 5, 7 and 9.

    Fig. 2-8. Track plan for staging yard throat

    The required code to align the turnouts using the software equivalent diode matrix is listed in Fig. 2-9. I have listed only the code for the upper yard, the odd number tracks, because once you see how it works it is easy to apply for any track arrangement. I am using the variable TB(  ) for the inputs from the Track alignment pushButtons and the variable SM(  ) for the outputs to control the Switch Motors.

    Using a computer, turnout alignment is very simple regardless of the complexity of the track arrangement or type of switch machine.  The computer simply reads the button pressed and uses its built-in software logic to set the appropriate turnouts. For example, look at the statement for Track 7. Rhetorically, it reads: If  Track Button 7 is pressed then Switch Motor 1 is set reversed, 2 is set reversed, 3 is set normal and 4 is set reversed.


        TBP = 1     'Turnout button pressed

        TUN = 1     ' Turnout normal alignment

        TUR = 2     'Turnout reverse alignment


        IF TB(1) = TBP THEN SM(1) = TUN

        IF TB(3) = TBP THEN SM(1) = TUR: SM(2) = TUN

        IF TB(5) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUR

        IF TB(7) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUN: SM(4) = TUR

        IF TB(9) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUN: SM(4) = TUN

    Fig. 2-9. Turnout control programming

    Note that the definitions of the turnout alignment constants, TUN and TUR, in Fig. 2-9, assume that the switch motor is directly connected to two output lines. Pull one line low, the turnout aligns ‘normal’. Pull the other line low the turnout aligns ‘reversed’. If a single output line is used to control the switchmotor, with a JLC provided SMC12 card, then redefine TUN = 0 and TUR = 1. That’s all there is to having the software control turnouts and the scheme works for any track arrangement.

    For example, on the SV Oregon System, we are using the software diode matrix approach to control the turnouts in 5 different double-ended freight classification yards, 2 different passenger terminals, 2 large double-ended staging yards and an entrance-exit interlocking plant. That adds up to a total of 236 track alignment buttons controlling 203 switch motors. The result is that at every location you simply press a single track alignment button and every turnout aligns toward the requested track. You just can’t beat the software diode matrix for simplifying operations – especially at large junctions, staging areas and classification yards. Pressing one button in Eugene Yard aligns the whole ladder to the requested track.

    Preventing Switch Throwing Under a Train

    However, the advantages of the C/MRI for these applications do not stop here. Let’s say you want to prevent turnouts from being thrown when a staging area throat is occupied. Simply add a couple more statements as shown in Fig. 2-10. It is very straightforward. You only need look to see IF OS(14) = occupied THEN skip over the statements that read the button presses and that set the turnouts! That’s all there is to using software to prevent throwing a turnout under a train.


        TBP = 1     'Turnout button pressed

        TUN = 1     'Turnout normal alignment

        TUR = 2     'Turnout reverse alignment

        CLR = 0     'Block clear

        OCC = 1     'Block occupied



        IF OS(14) = OCC THEN GOTO EXT  'Skip reading buttons if throat occupied

          IF TB(1) = TBP THEN SM(1) = TUN

          IF TB(3) = TBP THEN SM(1) = TUR: SM(2) = TUN

          IF TB(5) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUR

          IF TB(7) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUN: SM(4) = TUR

          IF TB(9) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUN: SM(4) = TUN


    Fig. 2-10. Programming to prevent throwing switches under train

    We used this procedure at every dispatcher controlled CTC powered turnout on the previous Sunset Valley as well as on the new SV Oregon System. Doing so emulates exactly what is done on the prototype to prevent accidentally throwing turnouts under a train. Software effectively “locks” the turnout’s position for the time period that the turnout is occupied.

    Using Figures 2-9 and 2-10 as examples, try setting up one of your own yard track arrangements to see how easy it is to program the computer to control turnouts and to prevent the switch points from being thrown when the turnout, or group of turnouts are occupied.

    Signaling a Terminal Throat

    It is natural, once turnouts are set and locked, to have the computer look at track occupancy to calculate and set the trackside signals. One way the software can set the exit signals from the terminal tracks is shown in Fig. 2-11. This program assumes there is a signal lever added to the panel; I call it SIGLEV, and that it must be set to LEFT to clear an exit signal. Also, OS(14) and BK(18) must be clear.

    The key to making the code easier is to define a track aligned variable. I call it TK and set it up in the calculate turnout alignment section. Basically, if the turnouts are aligned for Track 1 then variable TK = 1, for Track 3 then TK = 3, for Track 5 then TK = 5, for Track 7 then TK = 7 and for Track 9 then TK = 9. Using this approach, the TK variable is readily available during the signal calculation to use as a subscript to pick the correct signal number, i.e. the one to which the track is aligned.

    The programming in Fig. 2-11 follows very typical programming practice. Each time through the real-time loop all signals are initialized at red, or to red over red for two headed signals. Then for each signal, multiple conditions are checked in sequence to see if a more favorable condition is possible. As soon as a condition is found that keeps a given signal at stop, the program simply branches to calculate the next signal thus keeping the signal just calculated at its most restrictive indication.




      IF OS(14) = OCC THEN GOTO EXT  'Skip reading buttons if throat occupied

        IF TB(1) = TBP THEN SM(1) = TUN: TK = 1

        IF TB(3) = TBP THEN SM(1) = TUR: SM(2) = TUN: TK = 3

        IF TB(5) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUR: TK = 5

        IF TB(7) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUN: SM(4) = TUR: TK = 7

        IF TB(9) = TBP THEN SM(1) = TUR: SM(2) = TUR: SM(3) = TUN: SM(4) = TUN: TK = 9


    EXT: SW(1) = REDRED: SW(3) = REDRED: SW(5) = REDRED

         SW(7) = REDRED: SW(9) = REDRED



         IF OS(14) = OCC OR BK(18) = OCC THEN GOTO SIGEXT

         IF SIGLEV < > LEFT THEN GOTO SIGEXT    'Lever not equal left

         SW(TK) = REDYEL


     Fig. 2-11.  Programming exit signals at staging yard throat


    For special situations, I occasionally perform custom programming. For example I performed contract programming for a fellow railroader because he told me, “I want to put in a large C/MRI system, I can do the hardware but I need to hire someone to do the programming.” I was so busy at the time that I tried to talk him into doing the programming but he came back very strongly with, “I can never program, I've tried before...I don't understand it.....never will....It's beyond me.....etc.” I took the job, and working with the person I got part way through and once he saw how straightforward C/MRI programming was, he took over all the programming himself.  His comments changed to those like, “This programming my railroad is not bad at all....I still have a little problem now and then but for the most part everything works right away...when I do have to scratch my head for a bit, it’s wonderful to see the right performance evolve....I feel better having done it myself and then I really know how it works.” He then went on to program several additional railroads. One of my greatest joys is to see such personality changes brought on by the C/MRI experience. Contagiously, it becomes exciting to key in a few lines and watch things begin to work on the railroad!

    I hope by studying the above examples you will begin to see how easy it is to program the C/MRI to handle any signaling requirement including aligning and locking turnouts.


    Programs can be written in many different languages, but one of the most common and easy to understand languages for personal computers is BASIC. It is easy to learn and for many years a BASIC interpreter was included as an integral part of nearly every personal computer. On the other hand, earlier versions of BASIC have limitations for real-time operation with external hardware, which is, interacting with external hardware as it runs. Because many versions of Basic are strictly interpreted languages (not separately compiled into digital machine code), these versions of BASIC can be very slow in executing instructions. If you run into applications that demand higher program operational speed, it is best to move beyond an interpreted version of BASIC, but it is more than adequate for getting started.

    To speed up program development and operation, I recommend using one of the more advanced Basics. The two I like especially well are Microsoft QuickBASIC and Microsoft Visual Basic. QuickBASIC preceded Visual Basic so I will cover it first. The most universally applied version of Quick Basic is Version 4.5 and it is very suitable for C/MRI. QuickBASIC has a user-friendly editor that makes programming easier, it is well suited to real-time applications, capable of structured programming, no statement numbers are required and meaningful variable names can be applied. Fundamentally, I find it works very well for all real-time C/MRI programming applications not requiring a high level of graphic user interface coupled with extensive mouse and keyboard input. For those latter applications, Visual Basic is much better suited.

    Microsoft has dropped QuickBASIC as a product but this is not a problem because copies are readily available from a multitude of users and via the internet for zero cost. Likewise, the restriction that QuickBASIC must operate under DOS is not much of a disadvantage as most C/MRI users tend to dedicate somewhat older computers to the railroad rather than tying up their most powerful business or family computer. Alternatively, it is possible to use third-party DOS on more modern computers. Typically, high computer power is not important to most C/MRI applications.

    Although more expensive and slightly harder to learn, Visual Basic (VB) is an extremely popular language for C/MRI applications. VB operates under all versions of Windows and has many great graphics attributes.  Its major advantages shine for applications requiring extensive mouse and keyboard interfacing with pull down menus, dialog boxes, control buttons and extensive color graphics. Such capability is extremely important for modeling applications that emulate modern dispatching centers with computer generated track-train status monitoring displays. Actually, once you become familiar with using the Visual Basic structure, programming in Visual Basic is just as easy, or even easier, than programming in QuickBASIC. 

    Another useful language, PowerBASIC, operates under Windows. It is powerful, very fast and although it does not seem to have all the fancy bells and whistles of VB it seems well suited for more general C/MRI applications. I have no personal experience with Power Basic but if you are interested you can find more about it at www.powerbasic.com. Alternatively, as covered in the Railroader’s Application Handbook, there are many other versions of Basic that can be used for C/MRI applications. These include Liberty Basic, Just Basic, REAL Basic, Chipmunk Basic and Free BASIC.

    QuickBASIC should not be confused with QBasic, an interpreted Basic that came bundled with DOS 5.0 and higher. QBasic can be used for operating C/MRI, but it lacks the programming power and speed provided by higher-level compiler-based programs like QuickBASIC, Visual Basic, Power Basic, Pascal, Turbo Pascal, C, Turbo C, C++, Visual C++ and JAVA to name just a few. All work with the C/MRI.

    If you have a favorite programming language, then use it with the C/MRI. Any programming language providing access to serial I/O ports and basic IF-THEN type logic statements is usable with the C/MRI. If you are not familiar with programming, then BASIC is a good place to start. If BasicA, GW Basic or QBasic is installed on your machine then use it. If not, then I recommend you obtain a copy of Microsoft QuickBASIC Version 4.5 and/or a copy of Microsoft Visual Basic Version 6.0 or newer. Both work well for developing C/MRI applications. However, Visual Basic is definitely the better choice for applications seeking operations in the Windows environment where a high level of graphics coupled with mouse and keyboard input is desired. One nice feature is that if you do start out using QuickBASIC, and then find you have a desire to move up to Visual Basic, you will discover that almost all of your programming remains identical. In fact, in Chapter 16 I will show how easy it is to convert QuickBASIC programs to Visual Basic!

    As with any programming language, BASIC instructions vary a bit from one manufacturer to another. The two BASIC languages I use in this manual are Microsoft QuickBASIC V4.5 and Microsoft Visual Basic V6.0. The motto for all my programming is: Keep programming simple, straightforward and easy to understand. All my programs include extensive commenting so that reading the resulting code is much like reading the English language. The result is that these programs should be easy to convert to your favorite language, if this has not already been accomplished for you via the enclosed disk or via the C/MRI User’s Group.

    I cannot take the space to teach BASIC, QuickBASIC or Visual Basic or any other programming language in this manual, however most statements that we will need are easy to understand. Most languages you purchase come with a manual and computer stores have a wide assortment of books on most every programming language. One title I have always liked is BASIC BASIC. You can hardly get more basic than that!

    If you desire more information on Microsoft QuickBASIC, I highly recommend The Waite Group’s, MICROSOFT QuickBASIC BIBLE, published by Microsoft Press. Also, BASICs for DOS, by Gary Cornell, McGraw-Hill Publishing., provides excellent coverage of GW-BASIC, BasicA and Microsoft QBasic. Both books are out of print, but copies have been found through www.amazon.com and www.ebay.com. There are a hundreds of books available on Visual Basic. A good introductory book to get started with is Visual Basic 6 - Weekend Crash Course by Richard Mansfield (ISBN 0-7645-4679-1). Additional VB references are included in this manual at the end of Chapter 15.

    All Visual Basic examples operate with the C/MRI under a Windows environment. The QuickBASIC examples are written to operate under DOS. A software disk, enclosed with the User’s Manual, includes all the software presented in this manual using both QuickBASIC and Visual Basic. Be sure to start with the README file for a more detailed explanation of the disk’s content. Also make a working copy of the disk and save the original in a safe place prior to tailoring the programs to best fit your own needs.


    Independent of the language selected, every railroad device that is interfaced to the computer needs to be given a unique name for use by the software. Such unique names, within software, are typically referred to as symbol names or variables. In the C/MRI documentation, including this manual, I use the term variable.

    I like the term variable as it best represents the variable nature of the different railroad devices. For example, signals change between red, yellow and green. Turnouts change between normal and reverse. The signal levers on dispatcher CTC panels vary in position between left, stop and right.

    A key to making programming easy is selecting meaningful variable names to represent each railroad device. This was rather difficult using original versions of BASIC which limited you to two character variable names. However, most programming languages are much more lenient. For example, QuickBASIC lets you pick variable names with up to 40 alphanumeric characters in length. The first character must be a letter and you cannot include blank spaces but the alphabetical characters can be any combination of upper or lower case. The result provides very wide latitude in naming railroad devices. For example, you can use SIGNAL12, Signal12, SalemTurnout9, Turnout17, TURNOUT21, SignalLever192, or almost whatever else you desire.

    For convenience if you wish, you can elect to use subscripted variables like SignalEast(1), SignalEast(2), SignalEast(3) and so forth up to some defined maximum such as SignalEast(35). The number enclosed within the parentheses is referred to as the subscript or index. A DIMension statement is required to define the maximum range of each subscripted variable. In this case we would need to add the statement DIM SignalEast(35). When an error message “Subscript out of range” appears, it means that your subscript usage is larger than the size of the DIMension. If you use a subscripted variable without a corresponding DIMension statement, QuickBASIC defaults to a dimension of 10.

    Every variable is automatically allocated its own unique memory location within the computer. For example, every time QuickBASIC or Visual Basic encounters a new variable name within an application program, it assigns to it a unique memory location. Likewise, when QuickBASIC or Visual Basic encounters a DIM SignalEast(35) statement it reserves 35 memory locations to contain SignalEast( ). When an application program executes a statement containing SignalEast(I) for example, it is the value of I,  the subscript, enclosed within the parentheses that determines which SignalEast( ) is being addressed.

    Numerous programming languages let you include underscores within a variable name, such as Signal_East_12. Many programmers tend to use such very long concatenated variable names, for example, Dunsmuir_Signal_No._12_East. I personally find using such long names laborious to input via the keyboard, they are prone to making entry errors, they do not let you include much logic on a given coding line and the overall impact tends to clog up the program listing with a lot of unnecessary characters. I prefer using shorter more abbreviated, yet still meaningful, variable names. I typically select my variable names between 2 and 10 characters in length and usually all upper case. Some of the typical variable names I like to use are CLR for clear, OCC for occupied, RED for red, YEL for yellow, GRN for green, REDRED for red over red, SE( ) for signals east, SW( ) for signals west, BK( ) for block occupancy, SM( ) for switch motors, MAXTRIES for maximum tries before aborting inputs, and so forth.

    Where you have a whole bunch of similar devices such as signals, block occupancy detectors, switch motors, and so forth it is often easiest to simply number them consecutively as 1, 2, 3, 4 etc. and make use of subscripted variables such as SIG( ), BK( ) and SM(  ). On the other hand, if your railroad already happens to be documented using non-contiguous numbering, such as found on a dispatcher’s CTC machine, or on prototype intermediate block signal number plates (that are based upon milepost nomenclature), then subscript notation does not work very well. In these cases, you are better off using a unique variable name for each device.

    For example, reading from the SV’s Oregon System US&S CTC machine, selected variable names for the trackside signals can be written as; TS50RAB, TS50LA, TS50LB for the triad of signals at a typical prototype OS section, where the TS stands for Trackside Signal,  the R and L denote right or left facing signals on the CTC panel, and the A and B denote the signal head arrangement. The AB denotes a dual-head signal leading into the facing point end of a passing siding turnout. The A-only denotes a single-head mast signal at the frog end main track and the B-only denotes a dwarf leading out of the siding.

    Fundamentally, what I am trying to get across is that you can name your software variables representing each railroad device in any manner that is the most comfortable for you. Picking software variable names that correspond to your railroad’s wiring documentation, prototype layout and/or your control panel designations can provide significant advantages. I am biased, I must admit, but I recommend where feasible to stay close to those variable names I use in my numerous C/MRI example programs. Many additional recommended variable naming conventions are presented in the Railroader’s C/MRI Applications Handbook. In summary, choose a system and use it faithfully. The C/MRI software can easily handle whatever variable naming convention you prefer.