Unit SPI
Return to Unit Reference
Description
SPI (Serial Peripheral Interface) is a synchronous serial bus for communication with peripheral components.
The SPI protocol is not defined by any actual standard but some psuedo standards exist with all of the available devices. SPI is a master-slave protocol where the master asserts the chip selectline (CS) to select the slave device before sending data one byte at a time. For every byte written to the bus by the master the selected slave returns a byte as well so for every write there is an equivalent read. SPI can also operate in either 4 wire (standard) or 3 wire(bidirectional) modes.
Due to the lack of formal standards and the range of devices that exist various options are provided to allow setting clock phase and polarity as well chip select polarity.
For the purpose of this interface a device is the SPI controller attached to the local system and may be either a master or a slave. Since the protocol does not include any form of enumeration or identification the interface does not attempt to represent the devices connected to the bus, any driver written to communicate with a connected SPI device should know (or allow configuration of) the chip select for the for the device and the specific message format required for that device.
Constants
To be documented
Type definitions
To be documented
Public variables
To be documented
Function declarations
Initialization functions
procedure SPIInit;
| Note | Called only during system startup |
|---|
SPI functions
function SPIDeviceStart(SPI:PSPIDevice; Mode,ClockRate,ClockPhase,ClockPolarity:LongWord):LongWord;
| SPI | The SPI device to start |
|---|---|
| Mode | The device mode to set (eg SPI_MODE_4WIRE) |
| ClockRate | The clock rate to set for the device |
| ClockPhase | The clock phase to set (eg SPI_CLOCK_PHASE_LOW) |
| ClockPolarity | The clock polarity to set (eg SPI_CLOCK_POLARITY_LOW) |
| Return | ERROR_SUCCESS if completed or another error code on failure |
function SPIDeviceStop(SPI:PSPIDevice):LongWord;
| SPI | The SPI device to stop |
|---|---|
| Return | ERROR_SUCCESS if completed or another error code on failure |
function SPIDeviceWrite(SPI:PSPIDevice; ChipSelect:Word; Source:Pointer; Size,Flags:LongWord; var Count:LongWord):LongWord;
| SPI | The SPI device to write to |
|---|---|
| ChipSelect | The chip select for the slave to write to (eg SPI_CS_0) |
| Source | Pointer to a buffer of data to transmit |
| Size | The size of the buffer |
| Flags | The flags for this transfer (eg SPI_TRANSFER_DMA) |
| Count | The number of bytes written on return |
| Return | ERROR_SUCCESS if completed or another error code on failure |
| Note | Because SPI writes and then reads for each byte, received data will be discarded for each by written |
function SPIDeviceSetMode(SPI:PSPIDevice; Mode:LongWord):LongWord;
| SPI | The SPI device to set device mode for |
|---|---|
| Mode | The device mode to set (eg SPI_MODE_4WIRE) |
| Return | ERROR_SUCCESS if completed or another error code on failure |
function SPIDeviceSetClockRate(SPI:PSPIDevice; ClockRate:LongWord):LongWord;
| SPI | The SPI device to set clock rate for |
|---|---|
| ClockRate | The clock rate to set in Hz |
| Return | ERROR_SUCCESS if completed or another error code on failure |
Return to Unit Reference
