SPA Request message
The SPA Request message is structured as follows:
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
Com. | SPA TID | Index | Subindex | Offset | Res. | Data | |||||
Low | High | Low | High | LSB LO | LSB HI | MSB LO | MSB HI | ||||
The individual bytes have the following functions:
Byte | Name | Bit width | Function |
|---|---|---|---|
00 | Command | 8 | Control byte. The control byte is structured as follows:
The following supported SPA services are mapped in the control byte:
|
01 | SPA TID | 8 | Smart Parameter Access Transaction Identifier The byte for assigning the SPA Response message to the SPA Request message is assigned by the device and mirrored by the AS-Interface master. The device can determine whether the SPA Request message has been answered based on the SPA TID of the SPA Response message. The value is depicted in the SPA Response message. If the user changes the value for each message, the SPA Response message can be uniquely assigned to the SPA Request message via the SPA TID. |
02 – 03 | Index | 16 | Main index of the parameter |
04 | Subindex | 8 | Subindex of the parameter |
05 – 06 | Offset | 16 | Offset |
07 | Reserved | 8 | Reserved Reserved bytes must be set to 0. |
08 | Data | 8 | LSB LO – Low byte of the control word with low significance |
09 | 8 | LSB HI – High byte of the control word with low significance | |
10 | 8 | MSB LO – Low byte of the control word with high significance | |
11 | 8 | MSB HI – High byte of the control word with high significance |
