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0 software command structure, 0 software command structure -1 – Watlow 12LS Controller User Manual

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8-1

8.0 SOFTWARE COMMAND STRUCTURE

The 12LS will respond to commands according to the following format. The commands
generally follow the specifications of ANSI X3.28-1976. The structure is outlined below:

. Commands from Allen Bradley Programmable Controllers (CMD)

The A32PID will respond only to Unprotected Block Read (CMD01) and Unprotected Block
Write (CMD 08) commands from the Allen Bradley PLC. Any other command numbers received
will return an error status code.

. Error Checking (BCC / CRC)

Error checking is set on the global menu. The default is BCC and this has proven satisfactory in
most applications. CRC is recommended for highest data integrity, BCC provides slightly higher
speed.

. Protocol

Controller protocol is set for full duplex.

. Status Codes

Four Error Code numbers will be returned in the Status (STS) byte to denote the following error
conditions :

Error Code (Hex) Status/Error Condition
---------------- ----------------------
A0 Processor Reset
C0 Command Error
D0 Data Boundary Error
E0 [ Spare ]

Processor Reset

This Error Code is returned after :

- Power-up reset
- The watchdog timer resets the Master processor
- The Master processor resets the Slave processor

Command Error

This Error Code is returned when the 12LS receives a command that is not a Block Read or a
Block Write.