An example of a query to read coils 1 to 4 from the LD4 at address 2 is given below.
Field Name
Example (Hex)
Unit address
02
Function
01
Starting address Hi
00
Starting address Lo
00
Number of points Hi
00
Number of points Lo
04
Error check (LRC or CRC)
–
An example of a response is given below:
Field Name
Example (Hex)
Unit address
02
Function
01
Byte count
01
Data (coils 7 to 1)
04
Error check (LRC or CRC)
–
The status of the relay coils is shown in the Data 04 (hex) or binary 0100. Relay 1 is indicated by the
LSB. The status of the relays is therefore:
Relay 1 - OFF, Relay 2 - ON, Relay 3 - OFF, Relay 4 - OFF
Function 3 Read holding registers
This function reads the binary contents of the holding registers in the PM4 being addressed. The value
for this function is stored as a 32 but two's compliment number, 2 registers per channel are used. Note;
a value of 1,000,000 represents a positive overrange and -200,000 a negative overrange. Registers 1
to 2 hold the display value, registers 3 to 4 the valley memory (lowest reading in memory), registers 5 to
6 the peak memory (highest reading in memory), registers 7 to 8 the display hold value. Registers 9 to
16 hold the alarm high values for relays 1 to 4. Note a value of 0X8000 means that the relay is set to
OFF and has no high value. Registers 17 to 24 hold the alarm low values for relays 1 to 4. Note a value
of 0X8000 means that the relay is set to OFF and has no low value. Register 25 represents the decimal
point settings for the display.
An example of a query to read holding registers 1 to 3 from the TP488 at address 5 is given below.
Field Name
Example (Hex)
Unit address
05
Function
03
Starting address Hi
00
Starting address Lo
00
Number of points Hi
00
Number of points Lo
03
Error check (LRC or CRC)
–
An example of a response is given below:
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LD4LNMAN-1.0-1
