Chapter 6: Serial Communications
6.5.1 – Reading Holding Registers (Modbus Function 03)
This function is used to read a group of up to eight parameters from the SR44. The allowable
address range for this function is 0-127 for working parameters and 1000–1127 for offline EEROM
parameters.
Example – Modbus Function 03:
Read the fault history (P-73 – P-77) from SR44 slave #1 into a PLC
• Start Slave Address (SR44): 40074 *
• Start Master Address (PLC): internal PLC register 1
• Number of Elements: 3
Modbus Function 03 Transaction Table
Query
Response
Field
Hex Byte
Field
Hex Byte
Slave Address
01
Slave Address
01
Function
03
Function
03
Start Address High
00
Byte Count
04
Start Address Low *
4A (decimal = 74) *
Data High Byte
00 (P-73)
No. of Registers High 00
Data Low Byte
02 (P-74)
No. of Registers Low
02
Data High Byte
0D (P-75)
CRC Low
PLC & SR44 automatically
calculate CRC checksum values
Data Low Byte
0E (P-76)
CRC High
Data High Byte
10 (P-77)
Data Low Byte
C0 (P-78)
CRC Low Byte
PLC & SR44 automatically
calculate CRC checksum values
CRC High Byte
* The SR44 has a Modbus offset of one address for registers & bits; PLC targets one address higher.
SR44
씮
PLC
Parameter
Address / Byte *
Data Value
Hex
Data
Address ***
Decimal
Hex
P-73 (Last Trip)
40073 / high
0 (no trip)
00
00 02
internal PLC
register #1
P-74 (2nd Last Trip)
40073 / low
2 (too hot)
02
P-75 (3rd Last Trip)
40074 / high
13 (overload)
0D
0D 0E
internal PLC
register #2
P-76 (4th Last Trip)
40074 / low
14 (shearpin)
0E
P-77 (5th Last Trip)
40075 / high
16 (external trip)
10
10 C0
internal PLC
register #3
P-78 (Protection2) **
40075 / low **
192 (full+optimize)
C0
* SR44 Modbus addresses are variable.
Only the 1st address of the Function 03 read instruction ‘matches’ the parameter number, but
there is an offset of one address from the parameter#. If the PLC targets 40074, the PLC will
return data starting with P-73. P-73 will be in the high byte, and P-74 will be in the low byte.
** The Function 03 mutliple read instruction gets data from an even number of parameters.
Unwanted data can be discarded by the PLC.
*** PLC addresses are any valid user-assigned memory addresses.
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019
6–14
Содержание Stellar SR44
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Страница 66: ...Chapter 3 Applications BLANK PAGE SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019 3 22...
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Страница 194: ...Chapter 7 Optional Hardware BLANK PAGE SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019 7 6...
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