Compatibilities

Hardware

This type of communication is available for Premium PLCs via:

host slot of the processor and/or the TSX SCY 21601 module with:
- TSX SCP 111 PCMCIA card associated with the RS232 physical layer
- TSX SCP 112 PCMCIA card associated with 20 mA current loops
- TSX SCP 114 PCMCIA card associated with physical layers RS 422 and RS 485
built-in link with a TSX SCY 11601/21601 module associated with the RS485 physical layer

Software

The maximum frame size is 256 bytes.

The PCMCIA cards and the built-in link of the TSX SCY 11601/21601 can process 8 communication functions simultaneously in Modbus master.

The READ_VAR communication function can read up to 1000 consecutive bits in any remote device. To read in excess of 1000 bits, the SEND_REQ communication function must be used.

NOTE: Premium PLCs cannot send over 1000 bits following a read request.

NOTE: Be careful that two masters (on the same bus) do not send requests simultaneously otherwise the requests are lost and each report will have a bad result which could be 16#0100 (request could not be processed) or 16#ODFF (slave is not present).