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Cyclic Data Exchange
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Transfer length:
Cyclic only: 73 Bytes
Cyclic + RPC data: 128 Bytes
Baudrate:
at SPI: max. 10 MHz, usually 2 MHz.
Delay between cyclic transfer:
SPI: 0.5 ms... Heartbeat Timeout (1 second)
Minimal round-trip time: 4 ... 6 ms (depending on the used protocol and setup)
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Serial Peripheral Interface Timing and Settings
Following simplified diagram shows basic SPI timing which must be considered by the application controller.
Figure 3 Basic SPI timing
SPI Speed
The CC supports SPI speed in the range of 29.3 kHz to 10 theretically 20 MHz. Default SPI speed for most of the platforms is 2 MHz.
SPI Setup Time
In Figure 3 Basic SPI timing, the communication scheme between AC and CC is shown. Following time needs to be considered by the Application Controller during communication: the SPI Setup Time - the time between activation of the module using the Slave Select signal and first data - must be at least be 2-3 us, before the module accepts data over SPI.
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This time is the distance between two consecutive SPI transfers. Between two transfers a minimum time of 250 us must be kept to secure proper processing in the module.
SPI Settings
The module provides a management inferface, where initial configuration can be done. These properties can be stored permanently within the device. Following properties are provided to configure the SPI interface:
Variable | Description | Default value |
SPI_TYPE | SPI master/slave configuration | 1 = SLAVE |
SPI_MODE | SPI timing mode | 0 = MODE0* |
SPI_UNITWIDTH | SPI single transfer size | 0 = 8 BIT |
SPI_BITORDER | SPI bit transfer direction | 0 = MSB* |
SPI_TRANSFERSIZE | SPI packet transfer size | 128 |
* These Values can be modified
Cyclic Frame Structure
The cyclic frame must contain the structure from following table to get accepted by the iRJ45 module/ SoM.
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Byte 0..1 | Byte 2..5 | Byte 6 .. x | Byte x+1 .. x+4 | Byte x+5..x+8 | Byte x+9 | Byte x+10 | Byte (x+11) .. (x+14) |
|---|---|---|---|---|---|---|---|
Static Identifier | Data Length | Data | Function Id | RPC Id(little endian) | CTC Id | Flags | Fletcher-16 |
Table 22 RPC Request Structure
Byte 0..1 | Byte 2..5 | Byte 6 .. x | Byte x+1 | Byte x+2 | Byte (x+3)..(x+4) |
|---|---|---|---|---|---|
Static Identifier | Data Length | Response Data | CTC Id | Flags | Fletcher-16 |
Table 23 RPC Response Structure
Static Identifier
The 2 byte static identifier is used on the iRJ45 module to detect the start of a new RPC request or response. If the identifier is also contained in the data bytes the Fletcher-16 checksum will make sure that it don't gets threaded like an RPC request/response.
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