Despatch Protocol Plus Modbus Communications - Manual (Page 29)

Chromalox Instruments and Controls
A-51643 Rev. 6 10/06/03 23
Number of outputs hi $00
Number of outputs lo $07
CRC $----
Response
The input status in the response message is packed as one input per bit of the data field. Status is
indicated as 0 = Off, 1 = On. The LSB of the first data byte contains the input addressed in the query.
The other inputs follow toward the high order end of this byte, and from low order to high order in
subsequent bytes. If the returned input quantity is not a multiple of eight, the remaining bits in the final
data byte will be padded with zero (toward the high order end). The Byte Count field specifics the
quantity of complete bytes of data.
Example response:
Field Name Data
Slave address $08
Function $02
Byte count $01
Data (inputs 7 . . . 1) $74
CRC $----
5.2.3 [03] Read Holding Registers (Read Multiple Registers)
Class 0 command. Reads the contents of holding registers in the slave. Broadcast is not supported.
Query
The query message specifies the starting register and quantity of registers to be read. Registers are
addressed starting at 0.
Example: Request to read registers 108 . . . 110 from slave address 1.
Field Name Data
Slave address $01
Function $03
Starting address hi $00
Starting address lo $6B