Function 23: Writing and reading of several analog value outputs or inputs
A number of analog outputs can be written and a number of analog inputs read with one telegram using function 23. In this example the first 2 analog output words are written, and the first two analog inputs are read. The analog outputs start at offset 0x0800, while the inputs start at offset 0x0000. Here the offset always describes a word. Offset 0x0003 writes to the fourth word in the output process image. The length indicates the number of words, and the Byte count is formed from the combination of all the bytes that are to be written.
Example: 4 words - correspond to a byte count of 8
The data bytes contain the values for the analog outputs. In this example, two words are to be written. The first word is to receive the value 0x3FFF, and the second word is to receive the value 0x7FFF.
Query
|
Byte Name | Modbus RTU | Modbus ASCII | ||
|---|---|---|---|---|
Start - frame | - | - | ":" | 0x3A |
Address | 11 | 0x0B | "0B" | 0x30, 0x42 |
Function code | 23 | 0x17 | "17" | 0x31, 0x17 |
Read start address high | 0 | 0x00 | "00" | 0x30, 0x30 |
Read start address low | 0 | 0x00 | "00" | 0x30, 0x30 |
Read length high | 0 | 0x00 | "00" | 0x30, 0x30 |
Read length low | 2 | 0x02 | "02" | 0x30, 0x32 |
Write start address high | 8 | 0x08 | "08" | 0x30, 0x38 |
Write start address low | 0 | 0x00 | "00" | 0x30, 0x30 |
Write length high | 0 | 0x00 | "00" | 0x30, 0x30 |
Write length low | 2 | 0x02 | "02" | 0x30, 0x32 |
Byte Count | 4 | 0x04 | "04" | 0x30, 0x34 |
Data 1 high | 63 | 0x3F | "3F" | 0x33, 0x46 |
Data 1 low | 255 | 0xFF | "FF" | 0x46, 0x46 |
Data 2 high | 127 | 0x7F | "7F" | 0x37, 0x46 |
Data 2 low | 255 | 0xFF | "FF" | 0x46, 0x46 |
Error check, LRC/CRC |
| 0x76, 0xD3 | "12" | 0x31, 0x32 |
End - frame |
| t1-t2-t3 | CRLF | 0x0D, 0x0A |
Response
The Bus Coupler/Fieldbus Box responds with the start address and the length of the transferred bytes in the byte count. The data information follows. In this example the first word contains 0x0038 (hex) while the second word contains 0x3F0B.
|
Byte Name | Modbus RTU | Modbus ASCII | ||
|---|---|---|---|---|
Start - frame | - | - | ":" | 0x3A |
Address | 11 | 0x0B | "0B" | 0x30, 0x42 |
Function code | 23 | 0x17 | "17" | 0x31, 0x17 |
Byte Count | 4 | 0x04 | "04" | 0x30, 0x34 |
Data 1 high | 0 | 0x00 | "00" | 0x30, 0x30 |
Data 1 low | 56 | 0x38 | "38" | 0x33, 0x38 |
Data 2 high | 63 | 0x3F | "3F" | 0x33, 0x46 |
Data 2 low | 11 | 0x0B | "0B" | 0x30, 0x42 |
Error check, LRC/CRC |
| 0xF8, 0xA7 | "E3" | 0x45, 0x33 |
End - frame |
| t1-t2-t3 | CRLF | 0x0D, 0x0A |