using m-series PLC w/custom I/O rack

[Lsegelhorst]

I have been considering purchasing a starter kit to fullfill the need for a ladder logic solution to my situation...

I have a custom built I/O rack (from the component level up) this is connected to a PC via rs232.

the PC is running a basic program compiled w/QB45 this program reads the rs232 port and collects data from the I/O rack... processes the info, and writes a data string out to the serial port to the i/o rack.

heres the big question....

can the m-series PLC's be programmed to communicate via rs232 with my I/O rack, bypassing the PC altogether?
I would like to have a turn key setup and only use the computer to "load" the PLC.

I dont want to  re-wire the whole system... wich would be required if I where to eliminate my existing I/O rack.

this rack uses a protocall of our own design, and is not modbus capable. it is totaly unique.

actualy we have 2 of these racks connected together on the same serial line. both addressable by the PC

can the m-series plc do the communicating and the logic processing in place of the PC?

if so how should they be connected together?
rs232 to rs232 with the PLC as the host device?

  

[support]

You are trying to replace the PC with the T100MD PLC as the communication master. That shouldn't be too much of a problem especially if your own unique protocol is ASCII based and does not employ sophisticated error check (e.g. CRC32) beyond simple checksum or FCS.

The PLC has two independent serial ports. You can use the PRINT #n command to send ASCII string out of the serial port #n and INPUT$(n) to receive CR terminated string from serial port #n.

You can also use OUTCOMM n, d to send binary data out of serial port #n and INCOMM(n) to receive binary data. These four commands are good enough to implement your own master.

You can also use the NETCMD$ command with a "~" termination to automatically send out a custom ASCII string and wait to receive a response string from the slave.

You will not need to rewire your I/O rack at all. Of couse you will still need to rewrite the routine in our TBASIC to handle communication with the slave.

[Lsegelhorst]

Thank you for that helpfull information... you gave me confirmation of what I thought might be the case.

now my next question is will the PLC be able to hold my program...
of course I cant expect you to answer this without some more information such as amount of variable space, total sise of current program etc... I dont have this information as I did not do the programming for this system.

can you tell me what the capacities are of the available m-series units?

[support]

The PLC has 6K words of program memory and 1.7K words of non-volatile EEPROM data memory. Most of the TBASIC command takes from 1 to 3 words. I am not sure how big your program will be because it really depends on the amount of control and communication you have with the I/O racks and how efficient you structure your program.  The code size compiled by QB45  is not a good indication of the code size that will be in TBASIC because they works differently. What you can do is to download our educational version of TRiLOGI software, write some codes that may involve commuication with the I/O rack, and then select "Compile Only" and check the code size to determine if the PLC has sufficient memory to contain your entire program codes.