9.1.2.4 Serial Modbus Master Service
The current Modbus design supports the Master mode on all six serial ports. It is configurable at the port level as follows:
• Physical connection: RS-232, RS-422, RS-485
• Baud Rate: 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200
• Parity: none, odd, even
• Data Bits: seven, eight
• Stop Bits: one, two
• Station addresses
• Multidrop is applicable only to RS-485 with up to eight devices per port; maximum of 18 devices per board
• For RS-232 or RS-422, only one station is supported for these protocols
• RTU
• Time-out (milliseconds) per device
• 32–bit data Word ordering (for example, Least Significant Word [LSW] or Most Significant Word [MSW] first)
Note First denotes which word is in the lower-numbered register. All 16-bit registers are Big-Endian per standard
Modbus convention.
• Device response delay time
The Modbus service is configurable at the signal level as follows:
• Signal type
• Register number
• Read/write
• Transfer rate, 0.5, 1, 2, or 4 Hz
• Scaling: Raw min/max, Eng min/max
The service supports function codes 1-7, 15, and 16; it also supports double 16-bit registers for floating point numbers and
32-bit counters. It periodically (10 sec) attempts to reestablish communications with a dead station.
Type casting and scaling of all I/O signals to/from engineering units are supported on the PSCA and the ToolboxST*
application, for both fixed I/O and Modbus I/O.
288 GEH-6855_Vol_II GEH-6855_Vol_II Mark VIeS Functional Safety Systems Volume II
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