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AB to AD - Communication

I will review the serial port communication capabilities. Ethernet and industry standard I/O protocols (as slave only) are also available with add-on modules. I will not discuss them.

Hardware View

Port 1 – RS232 serial, RJ11 connector, contains power pins for hand held programmer unit and simple displays.

Port 2 – Adds RS422/RS485 capability and hardware handshaking lines if needed. DE15 (high density 15 pin) plug. I recommend the DN-15TB  wiring block to break out the wires to screw terminals. This includes switches for inserting termination resistors and indicator lights. (Note, this unit is now obsolete.  Use the ZL-CMA15 - it comes with or without signal indicator LEDs.)

The manual has good drawing explaining the hardware hook up of these ports.

Protocol View

Port 1 – K-sequence (slave only), DirectNET (slave only), MODBUS (slave only)

Port 2 – K-sequence (slave only), DirectNET (master/slave), MODBUS RTU (master/slave) and non-sequence protocols PRINT, ASCII In, ASCII Out.


  • K-sequence – optimized for programming and monitoring.
  • DirectNET – optimized for PLC to PLC communications.
  • MODBUS RTU – industry standard – very compact protocol
  • PRINT – the DL06 has very flexible string output instructions
  • ASCII In/Out – this may be better left to an add-on BASIC card especially for complex received string interpretation

A plea for sanity – MODBUS

If you need to use the CPU as a MODBUS master PLEASE use the DL06 or the DL260 CPUs. These include MODBUS specific instructions (MWX and MRX). Other CPUs can use MODBUS but the MODBUS references must be translated into equivalent memory references in an AD CPU. If you try to refer to the written conversion method you WILL GO INSANE. AutomatonDirect has tried to make this a little less painful by making an Excel spreadsheet to do the conversions (refer to here: AN-MISC-010 Note the instructions in Workbook 1 if using Excel. I use which has no problem.). If you are using an external device as a Modbus master to get information from the PLC then you must use the application note for reference.

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Copyright © 2005, 2006, 2007 Bernard Carlton