really=20
            great. None of this matters much until you're trying to run =
dozens=20
            of rungs of logic with fast cycle times.</P>
            <P>I support the A/D converter, PWM unit, and UART on those=20
            microcontrollers that provide them. That means that you can =
write=20
            ladder logic that reads analog inputs, and that sends and =
receives=20
            characters over serial (for example to a PC, if you add a =
suitable=20
            level-shifter like a MAX232, or to a character LCD). It is =
possible=20
            to send arbitrary strings over serial, as well as the values =
of=20
            integer variables, as ASCII text. Finally, I now support =
=91preserved=20
            variables=92 on devices with EEPROM; you can indicate that a =

            particular variable should be auto-saved to nonvolatile =
memory=20
            whenever it changes, so that its value is persistent across =
power-on=20
            resets.</P>
            <H3>Limitations, and Disclaimer</H3>
            <P>Of course a microcontroller with this software can't do=20
            everything that a PLC will. Most PLC environments offer more =

            features and predefined blocks than my tool does. The PLC =
hardware=20
            is better too; usually the inputs and outputs are designed =
to=20
            withstand incredible electrical abuse. You can get a =
PIC16F877 on a=20
            carrier board for ten or twenty USD, though, and you'll pay =
a fair=20
            bit more for a PLC with the same capabiltities.</P>
            <P>So far I have received very few bug reports compared to =
the=20
            number of people with questions or feature requests. There =
is still=20
            great possibility for defects, especially in the targets for =

            microcontrollers that I do not physically have (and =
therefore cannot=20
            test). Certainly do not use LDmicro for anything =
safety-critical, or=20
            anything that would break something expensive if it =
failed.</P>
            <P>As noted above, the code that it generates is far from =
optimal.=20
            Also, not all of the data RAM in PIC16 devices is available =
to the=20
            ladder logic program. This is because I have not implemented =
very=20
            much support for all the paging nonsense. I do, however, =
support the=20
            program memory paging, which is necessary to access program =
memory=20
            locations in the PIC16 beyond 2k.</P><A name=3Ddl></A>
            <H3>Download</H3>
            <P>The software is tested under Windows XP. Unconfirmed =
reports=20
            suggest that it works under Windows 98. The download is a =
.exe file;=20
            there are no other files required, so there is no =
installation=20
            program. Save it somewhere on your computer and just run it, =
and it=20
            will work. The manual is included in the .exe file, but you =
can=20
            download it separately if you want.</P>
            <P>The compiler generates Intel IHEX files. Most of the =
programming=20
            software that I have seen expects this. Of course you need =
some sort=20
            of programming gadget to get the hex file into the chip. For =
the=20
            AVRs, I recommend an STK300-type parallel port dongle, like =
<A=20
            href=3D"http://www.olimex.com/">Olimex</A> sells. For the =
PICs, I=20
            recommend Microchip's PICkit 2, which is available from =
their <A=20
            href=3D"http://buy.microchip.com/">web store</A>.=20
            <P>I would appreciate any bug reports. The following chips =
are=20
            supported and tested:</P>
            <P>
            <UL>
              <LI>PIC16F877=20
              <LI>PIC16F876=20
              <LI>PIC16F628=20
              <LI>ATmega64=20
              <LI>ATmega128 </LI></UL>
            <P></P>
            <P>The following chips are supported but not tested; they =
should=20
            work, but no guarantees. If you try one and it works then I =
would=20
            appreciate a success report: </P>
            <P>
            <UL>
              <LI>PIC16F88=20
              <LI>PIC16F819=20
              <LI>ATmega162=20
              <LI>ATmega32=20
              <LI>ATmega16=20
              <LI>ATmega8 </LI></UL>
            <P></P>
            <P>It is also possible to generate C code from the ladder =
program.=20
            That is less convenient, but you could use it on any =
processor for=20
            which you have a C compiler.</P>
            <P>LDmicro can generate interpretable byte code. If you are =
willing=20
            to write an interpreter then you can use this to run your =
ladder=20
            code on any kind of target. There is not very much =
documentation on=20
            this, but I provide a sample interpreter in mostly-portable =
C.</P>
            <P>Here is the program:</P>
            <P>
            <UL>
              <LI><A =
href=3D"http://cq.cx/dl/ldmicro.exe">ldmicro.exe</A>=20
              (program, release 1.5)=20
              <LI><A =
href=3D"http://cq.cx/dl/ldmicro.txt">ldmicro.txt</A> (manual)=20

              <LI><A =
href=3D"http://cq.cx/dl/ldmicro-changes.txt">feature/bugfix=20
              history</A>=20
              <LI>sample: <A href=3D"http://cq.cx/dl/traffic.ld">a =
simplified=20
              traffic light</A>=20
              <LI>sample: <A =
href=3D"http://cq.cx/dl/7seg-display.ld">how to drive=20
              a seven-segment display</A>=20
              <LI>sample: <A href=3D"http://cq.cx/dl/hello.ld">=91hello, =
world;' it=20
              prints the string over serial</A>=20
              <LI><A href=3D"http://cq.cx/dl/ldinterpret.c">sample =
bytecode=20
              interpreter</A> / <A =
href=3D"http://cq.cx/dl/intcode.h">needed=20
              header</A> </LI></UL>
            <P></P>
            <P>(right-click to save any of these files)</P>
            <P><B>Please report any defects.</B> This is freeware, with =
no=20
            department in charge of quality control. I do not even have =
the=20
            hardware to test many of the targets myself. A bug that is =
not=20
            reported is unlikely to ever be fixed.</P>
            <P>I have a <A=20
            =
href=3D"http://cq.cx/ladder-tutorial.pl"><B>tutorial,</B></A> in which=20
            I describe how to enter a simple ladder diagram, simulate =
it, and=20
            then generate an IHEX file and program it into a PIC. That =
is=20
            probably the easiest way to get started with this =
software.</P>
            <P>The source code for LDmicro is not generally available. =
If you=20
            would like access to the source code, or if you are =
interested in a=20
            customized version of LDmicro, then please <A=20
            href=3D"http://cq.cx/contact.pl">contact me</A> with your=20
            requirements.</P>
            <P><I>April 2007, Cambridge MA</I></P>
            <P></P><BR><IMG height=3D10=20
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