Modbus 0X Implementation Features; Figure 5-15. Example Transaction Request For Eight Physical Output Coils; Figure 5-16. Example Of Raw Data Decode - ABB TPU2000 Technical Manual

Figure 5-15. Example Transaction Request for Eight Physical Output Coils

Modbus 0X Implementation Features

Modbus is a protocol often used in the industrial sector. The protocol was developed to operate between hosts
and programmable logic controllers. The controlling device, in most cases was a PLC (Programmable Logic
Controller), which had the capability of detecting and storing fast events and indicating to the polling device that
an event had occurred. The change detect feature was not part of the protocol, but part of the monitoring device
(namely the Modicon PLC).
Utility devices require that no event is to be missed in the field IED. ABB has incorporated two methods in which
a device is notified that events have occurred in the field IED between host polls. The two methods employed for
0x data (Modbus Function Code 01) are:
MOMENTARY CHANGE DETECT
LATCHED ELEMENT RETENTION
MOMENTARY CHANGE DETECT and LATCHED ELEMENT RETENTION are independent of the protocol.
These ABB innovations allow Modbus protocol to address and satisfy the concerns common to a utility
TPU2000/2000R Modbus/Modbus Plus Automation Guide
Example - Read Output 1-6
Obtain Output 6 Through Output 1 Status Indication (00271 to 00266 per the memory map). ( MODBUS RTU Ex.)
Host Sends : 01 01 01 08 00 06 3C 36
IED Addr = 01
Function = 01
Data Start Address = 01 08 ( which is 266-1 in hex =010A)
Amount of Data Requested = 6 Coils
CRC-16 Checksum = 3C 32 Hex
Note: RTU does not code data in ASCII header and trailer is three character delays.
Relay Responds:01 01 01 21 91 90
IED Addr = 01
Function = 01
Data Bytes Received = 1
Data Received = 21
CRC-16 Checksum = 91 90 Hex
Function 01- Read Coil Status
Example - Analysis of Data Received
2 1
0 0 1 0 0 0 0 1
Padded 0
Padded 0
000271 Out 1 Status
000270 Out 2 Status
000269 Out 3 Status
000268 Out 4 Status
000267 Out 5 Status
000266 Out 6 Status
RESULT : Output 1 and Output 6 are energized.

Figure 5-16. Example of Raw Data Decode

Modbus Slave Addr =1
E C
Read from
0X Mapping
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