Automationdirect.com Stellar SR44, User Manual

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6–15
6.5.2 – Writing Single Coil (Modbus Function 05)
This function is used to set or clear a single bit within the Read/Write parameters between 0
through 127. (Only the bits within parameters designated as Read/Write can be preset with this
function; Parameters 18, 51, 52, 53, 54, 86, 95, 96, 121, & 127)
Example – Modbus Function 05:
PLC writes “Select 2nd Parameter Group” to SR44 (send a value of 1 to Bit#6 of P-52):
• Start Slave Bit Number (SR44): 423*
• Start Master Address (PLC): internal PLC bit address #1 (value = 1)
Modbus Function 05 Transaction Table
Query Response
Field Hex Byte Field Hex Byte
Slave Address 01 Slave Address 01
Function 05 Function 05
Bit Address 1A7 (decimal = 423) * Bit Address 1A7 (bit 422*) (bit 06 of P-52)
Force Data 01 (select 2nd parameter set) Force Data 01 (select 2nd parameter set)
CRC Low
PLC & SR44 automatically
calculate CRC checksum values
CRC Low Byte
PLC & SR44 automatically
calculate CRC checksum values
CRC High CRC High Byte
* SR44 has a Modbus offset of one address for registers & bits; PLC targets one address higher.
SR44
씯
PLC
Parameter Bit Address *
Data Value
Hex
Data
Address **
Decimal Hex
P-52 / Bit 06
Second Parm Set
423 * 1 1 1
internal PLC
bit address #1
* SR44 bit addresses have an offset of one address from the parameter bit#.
The PLC needs to target slave bit #423 in order to change bit #422.
** PLC addresses are any valid user-assigned bit addresses.
Chapter 6: Serial Communications
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019