Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 39)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 39
3.8. Modbus Compatibility
The Communication Interface supports the following Modbus RTU commands.
Read Coil Status
Read Input Status
Read Holding Registers
Read Input Registers
Force Single Coil
Preset Single Register
Force Multiple Coils
Preset Multiple Registers
Modbus 08 Command sub-function 0
The following coil and register mappings, as dictated by the Modbus protocol, are supported by the
Communications Interface.
00001 - 10000 coils (10000 coils) read/write
10001 - 20000 digital inputs (10000 digital inputs) read only
30001 - 40000 input registers (10000 input registers) read only
40001 - 50000 holding registers (10000 holding registers) read/write
Each individual coil or register may be set to read only by checking the Write Protect option in the
variable’s Extended Attributes, overriding the Modbus read/write capability. If an external Modbus
master subsequently writes to a protected coil or register, the new data value will be ignored.
The other Extended Attributes are described in PD-8082.
3.8.1. Modbus Write Protection Compatibility
To allow for compatibility with previous versions of the module firmware, which has fixed blocks of write
protected coils and registers, there is a configuration option available that reasserts this protection.
When the block protection is enabled, the read/write capability of the coils and registers are defined as
follows:
00001 – 7500 coils (7500 coils) read only
07501 - 10000 coils (2500 coils) read/write
40001 - 47500 holding registers (2500 holding registers) read only
47501 - 50000 holding registers (2500 holding registers) read/write
The Communications Interface does not support duplicate Modbus addresses.