La Función de LDmicro

NTRODUCTION

============

LDmicro generates native code for certain Microchip PIC16 and Atmel AVR

microcontrollers. Usually software for these microcontrollers is written

in a programming language like assembler, C, or BASIC. A program in one

of these languages comprises a list of statements. These languages are

powerful and well-suited to the architecture of the processor, which

internally executes a list of instructions.

PLCs, on the other hand, are often programmed in `ladder logic.' A simple

program might look like this:

|| ||

|| Xbutton1 Tdon Rchatter Yred ||

1 ||-------]/[---------[TON 1.000 s]-+-------]/[--------------( )-------||

|| | ||

|| Xbutton2 Tdof | ||

||-------]/[---------[TOF 2.000 s]-+ ||

|| ||

|| ||

|| ||

|| Rchatter Ton Tnew Rchatter ||

2 ||-------]/[---------[TON 1.000 s]----[TOF 1.000 s]---------( )-------||

|| ||

|| ||

|| ||

||------[END]---------------------------------------------------------||

|| ||

|| ||

(TON is a turn-on delay; TOF is a turn-off delay. The --] [-- statements

are inputs, which behave sort of like the contacts on a relay. The

--( )-- statements are outputs, which behave sort of like the coil of a

relay. Many good references for ladder logic are available on the Internet

and elsewhere; details specific to this implementation are given below.)

A number of differences are apparent:

* The program is presented in graphical format, not as a textual list

of statements. Many people will initially find this easier to

understand.

* At the most basic level, programs look like circuit diagrams, with

relay contacts (inputs) and coils (outputs). This is intuitive to

programmers with knowledge of electric circuit theory.

* The ladder logic compiler takes care of what gets calculated

where. You do not have to write code to determine when the outputs

have to get recalculated based on a change in the inputs or a

timer event, and you do not have to specify the order in which

these calculations must take place; the PLC tools do that for you.

LDmicro compiles ladder logic to PIC16 or AVR code. The following

processors are supported:

* PIC16F877

* PIC16F628

* PIC16F876 (untested)

* PIC16F88 (untested)

* PIC16F819 (untested)

* PIC16F887 (untested)

* PIC16F886 (untested)

* ATmega128

* ATmega64

* ATmega162 (untested)

* ATmega32 (untested)

* ATmega16 (untested)

* ATmega8 (untested)

It would be easy to support more AVR or PIC16 chips, but I do not have

any way to test them. If you need one in particular then contact me and

I will see what I can do.

Using LDmicro, you can draw a ladder diagram for your program. You can

simulate the logic in real time on your PC. Then when you are convinced

that it is correct you can assign pins on the microcontroller to the

program inputs and outputs. Once you have assigned the pins, you can

compile PIC or AVR code for your program. The compiler output is a .hex

file that you can program into your microcontroller using any PIC/AVR

programmer.

LDmicro is designed to be somewhat similar to most commercial PLC

programming systems. There are some exceptions, and a lot of things

aren't standard in industry anyways. Carefully read the description

of each instruction, even if it looks familiar. This document assumes

basic knowledge of ladder logic and of the structure of PLC software

(the execution cycle: read inputs, compute, write outputs).

ADDITIONAL TARGETS

==================

It is also possible to generate ANSI C code. You could use this with any

processor for which you have a C compiler, but you are responsible for

supplying the runtime. That means that LDmicro just generates source

for a function PlcCycle(). You are responsible for calling PlcCycle

every cycle time, and you are responsible for implementing all the I/O

(read/write digital input, etc.) functions that the PlcCycle() calls. See

the comments in the generated source for more details.

Finally, LDmicro can generate processor-independent bytecode for a

virtual machine designed to run ladder logic code. I have provided a

sample implementation of the interpreter/VM, written in fairly portable

C. This target will work for just about any platform, as long as you

can supply your own VM. This might be useful for applications where you

wish to use ladder logic as a `scripting language' to customize a larger

program. See the comments in the sample interpreter for details.

COMMAND LINE OPTIONS

====================

ldmicro.exe is typically run with no command line options. That means

that you can just make a shortcut to the program, or save it to your

desktop and double-click the icon when you want to run it, and then you

can do everything from within the GUI.

If LDmicro is passed a single filename on the command line

(e.g. `ldmicro.exe asd.ld'), then LDmicro will try to open `asd.ld',

if it exists. An error is produced if `asd.ld' does not exist. This

means that you can associate ldmicro.exe with .ld files, so

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