Despatch Protocol Plus Modbus Communications - Manual (Page 12)

Chromalox Instruments and Controls
A-51643 Rev. 6 10/06/03 6
3 Register and I/O Mapping
3.1 Unmapped and Reserved Registers
Reserved and NA registers will be read as zero with no exception error being generated. Thus, the host
can request data from multiple addresses with gaps between and still receive a valid response. Illegal and
undefined register address blocks will always generate an illegal data address exception.
Reserved and NA registers may be written without generating an exception, however the data is ignored
for these registers and no write takes place. Illegal and undefined register address blocks will always
generate an illegal data address exception.
3.2 Register Quantity Limitations
The number of registers that can be accessed in one query is limited to 50.
3.3 Discrete Input Assignments
The status of the four event inputs can be read as discrete inputs in Modbus format.
Table 3: Protocol
TM
Plus Discrete Input Address Map
Data Address Hex Address Description Security
0
$0000 Event Input 1
0
1
$0001 Event Input 2
0
2
$0002 Event Input 3
0
3
$0003 Event Input 4
0
4 -- 7
$0004 -- $0007 Illegal, Reserved for future inputs
0
8 -- 65535
$0008 - $FFFF Undefined, available for application assignment
0
3.4 Discrete Output Assignments
The status of the four relay outputs can be read as discrete outputs in Modbus format. Writes to the
outputs are not supported, that is, the functions ―Write Single Output‖ (06) and ―Write Multiple Outputs‖
(15) are not implemented.