Function 8: Diagnosis
The diagnosis function provides a series of tests for checking the communication system between the master and the slave and for examining a variety of internal error states within the slave. A broadcast telegram is not supported.
The function in the query uses a subfunction code field of two bytes to define the type of test to be carried out. The slave outputs the function code and the subfunction code in a response.
The diagnostics queries use a two-byte data field to send diagnostics data or control information to the slave.
Query
|
Byte Name | Modbus RTU | Modbus ASCII | ||
|---|---|---|---|---|
Start - frame | - | - | ":" | 0x3A |
Address | 11 | 0x0B | "0B" | 0x30, 0x42 |
Function code | 8 | 0x08 | "08" | 0x30, 0x38 |
Subfunction high | 0 | 0x00 | "00" | 0x30, 0x30 |
Subfunction low | 0 | 0x00 | "00" | 0x30, 0x30 |
Data high | 2 | 0x02 | "02" | 0x30, 0x32 |
Data low | 3 | 0x03 | "03" | 0x30, 0x33 |
Error check, LRC/CRC |
| 0xA1, 0xC0 | "E8" | 0x45, 0x38 |
End - frame |
| t1-t2-t3 | CRLF | 0x0D, 0x0A |
Response
|
Byte Name | Modbus RTU | Modbus ASCII | ||
|---|---|---|---|---|
Start - frame | - | - | ":" | 0x3A |
Address | 11 | 0x0B | "0B" | 0x30, 0x42 |
Function code | 8 | 0x08 | "08" | 0x30, 0x38 |
Subfunction high | 0 | 0x00 | "00" | 0x30, 0x30 |
Subfunction low | 0 | 0x00 | "00" | 0x30, 0x30 |
Data high | 2 | 0x02 | "02" | 0x30, 0x32 |
Data low | 3 | 0x03 | "03" | 0x30, 0x33 |
Error check, LRC/CRC |
| 0xA1, 0xC0 | "E8" | 0x45, 0x38 |
End - frame |
| t1-t2-t3 | CRLF | 0x0D, 0x0A |
Mirroring a request (subfunction 0)
Subfunction 0 causes the data that is sent to the slave by the master to be returned.
Coupler Reset (Subfunction 1)
The Bus Coupler/Fieldbus Box is reinitialized with subfunction 1, error counters are reset, and the Bus Coupler/Fieldbus Box carries out a self-test. During the time, in which the Bus Coupler/Fieldbus Box is reset, no telegrams are received or sent.
 | Response with subfunction 1 Before the Bus Terminal Controller restarts, it sends a response with subfunction 1. |
| Subfunctions 0 and 1 The BC8150 has subfunctions 0 and 1 implemented. All other subfunctions return "0". |
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 01 | 00 00 | 00 00 |
Delete all counter contents (Subfunction 10)
If this subfunction is called, the Bus Coupler/Fieldbus Box deletes all error counters.
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 0B | 00 00 | Echo query data |
Bus communication response counter (subfunction 11)
Returns the number of communication answers.
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 0C | 00 00 | Counter value |
CRC error counter (subfunction 11)
Indicates the number of detected CRC errors
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 0D | 00 00 | Counter value |
Error response counter (subfunction 13)
This counter indicates the number of error response telegrams, which the Bus Coupler/Fieldbus Box has sent.
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 0D | 00 00 | Counter value |
The following functions contain the counter states for various units. This means that the Modbus telegrams can be distinguished through units, for example when the Bus Coupler/Fieldbus Box is accessed from different masters.
Slave responses (subfunction 14)
Contains the number of answers that the slave has sent.
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 0E | 00 00 | Counter value |
Number of unanswered telegrams (subfunction 15)
Contains the number of answers that the slave has not sent.
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 0F | 00 00 | Counter value |
Number of error responses (subfunction 16)
Contains the number of error answers that the slave has sent.
|
Subfunction | Data field (query) | Data field (response) |
|---|---|---|
00 10 | 00 00 | Counter value |