Read complete array or record (FC102)
This function code is used read complete array or record of the object dictionary.
To start/restart array readout, sub-function code 55h has to be sent. This code would always reset the transmission to the object with sub-index 00h. All following requests have to have the sub-function code AAh. At the end, when all the subentries of the array have been read, an exception response is generated.
The format of each object read is as follows:
| Name | Length | Value / Remark |
|---|---|---|
| Slave Address | 1 Byte | |
| Function Code | 1 Byte | 66h |
| Sub-function code | 1 Byte | 55h or AAh |
| Length of data | 1 Byte | 00h |
| Index of array | 2 Bytes | |
| CRC | 2 Bytes |
| Usage | Length | Value / Remark |
|---|---|---|
| Slave Address | 1 Byte | |
| Function Code | 1 Byte | 66h |
| Subfunction Code | 1 Byte | |
| Length of data (without CRC) | 1 Byte | |
| n times a Object dictionary frame | 1 - 252 Bytes | |
| CRC | 2 Bytes |
| Name | Length | Value / Remark |
|---|---|---|
| Index Low | 1 Byte | |
| Index High | 1 Byte | |
| Sub-index | 1 Byte | |
| No. of data bytes | 1 Byte | Number m of valid bytes in data field |
| Data byte | m-1 Byte |
Example
The following numbers are written in hexadecimal., the index of the object to read is 2400h. The slave address is "5"h.
Start read array with the request
The response is
Error reaction
In case of an error, the following message will be sent:
| Name | Length | Example value |
|---|---|---|
| Slave Address | 1 Byte | |
| Function code | 1 byte | 2Bh +80h (171d = 43d + 128d) (indicates error) |
| Modbus exception code | 1 byte | FFh (extended exception) |
| Extended exception length | 2 bytes | 6 |
| MEI type | 1 byte | 0Dh |
| Exception code | 1 byte | CEh |
| Error code | 4 bytes | CANopen error code |
| CRC | 2 Bytes |
In case an not supported control option bit is set, the following error message will be sent:
| Name | Length | Example value |
|---|---|---|
| Slave Address | 1 Byte | |
| Function code | 1 byte | 2Bh +80h (171d = 43d + 128d) (indicates error) |
| Modbus exception code | 1 byte | FFh (extended exception) |
| Extended exception length | 2 bytes | 2 + length of Supported protocol control |
| MEI type | 1 byte | 0Dh |
| Exception code | 1 byte | AEh |
| Supported protocol control | 1 or 2 bytes | See following table |
| CRC | 2 Bytes |
| Bit | Field name | Description |
|---|---|---|
| 0 | Extend flag | This bit is used when the object dictionary data set is larger than what fits in one Modbus command. The data set is then extended over multiple Modbus messages, each message being a fragment of the data set. "0" = No multiple message transaction, or end of multiple message transaction; "1" = Part of a multiple message transaction |
| 1 | Extend protocol control | Length of protocol control, the value "0" indicates a length of 1 byte, the value "1" a length of 2 byte |
| 2 | Counter byte option | This bit is set to 1 to indicate that the counter byte field is used in this message. If this bit is set to 0 the counter byte does not exist in this message. |
| 3 and 4 | Reserved | 0 |
| 5 | Network ID option | Not supported, must be "0". |
| 6 | Encoded data option | Not supported, must be "0". |
| 7 | Access flag | This bit indicates the access method of the request command, "0" = read, "1" = write |
| 8 to 15 | Reserved | 0 |
The following example shows an error in case of a wrong request. The requests reads the object 6061h:00 with a length of 2 byte, but the object is 1 byte long, actually:
- Request
- Response
