This version (06 Oct 2011 16:37) was approved by Jean McAdam.
SPI: Serial Port Interface
The SPI interface on the SDP is a full duplex, synchronous serial interface. The SDP is the Master for all SPI transfers. When an SPI transfer occurs, data is simultaneously transmitted as new data is received. The SPI_CLK signal synchronises the shifting of data out and the sampling of data in on the two serial data pins (MOSI and MISO).
| Pin # | Pin SDP 120 Pin Connector Name | Description |
|---|---|---|
| 82 | SPI_CLK | SPI Serial Clock |
| 83 | SPI_MISO | SPI Master In Slave Out |
| 84 | SPI_MOSI | SPI Master Out Slave In |
| 85 | SPI_SEL_A | SPI Slave Select 1 |
| 37 | SPI_SEL_B | SPI Slave Select 2 |
| 38 | SPI_SEL_C | SPI Slave Select 3 |
Table 1: SPI Pin Assignments
The SPI protocol supports four different combinations of serial clock and polarity modes, SPI Modes 0, 1, 2 & 3.
| Mode | CPOL, Clock Polarity | CPHA, Clock Phase |
|---|---|---|
| 0 | 0 | 0 |
| 1 | 0 | 1 |
| 2 | 1 | 0 |
| 3 | 1 | 1 |
Table 2 : SPI Modes
Figure 1 : SPI Modes Explained
The maximum clock frequency for SDP-S SPI transfers is 10MHz.
The maximum frame frequency for SDP-S SPI transfers is shown below…
| Transfer size | Frame Freq Max | |||
|---|---|---|---|---|
| SPI Write, WriteRead | SPI Read | |||
| Mode 0,2 | Mode 1,3 | Mode 0,2 | Mode1,3 | |
| 8 bits | 500kHz | 465.1kHz | 456.6kHz | 450.4kHz |
| 16 bits | 323.6kHz | 308.6kHz | 310.5kHz | 307.6kHz |
| 24 bits | 255.1kHz | 245.7kHz | 246.9kHz | 245kHz |
| 32 bits | 210kHz | 203.6kHz | 204.4kHz | 203.2kHz |
Table 3: SPI Frame Frequency Limits
SPI Timing Examples
These timing examples are estimated and not guaranteed to be an exact reflection of the interface timing. These examples were generated for a 10MHz SCLK and the delays listed are the estimated maximum times.
Figure 2 : SPI transfer protocol, CPHA = 0, 8 bit data
Figure 3 : SPI transfer protocol, CPHA = 1, 8 bit data
Figure 4 : SPI transfer protocol, CPHA = 0, 16 bit data
Figure 5 : SPI transfer protocol, CPHA = 1, 16 bit data
Figure 6 : SPI transfer protocol, CPHA = 0, >16 bit data
Figure 7 : SPI transfer protocol, CPHA = 1, >16 bit data
SPI Extended Interfaces for converters
This section introduces timing diagrams for interfacing to ADI parts that requires Busy or Ready signals combined to CS to decode the part. The singularity of these modes is that the MISO line provides double functionality, data and ready signal.
The serial interface can operate in 3-wire mode by tying CS low. The end of conversion can be monitored using RDY and/or Busy. The DOUT/RDY pin functions as a data ready signal also, with the line going low when a new data-word is available in the output register.
Given the complexity of the implementation, the description below provides an additional explanation of how these interfaces are programmed to be used within the SDP.
Figure 8 : Single Read more with RDY
Figure 9 : Single Conversion Mode with RDY (AD7190 example)
| LabVIEW Implementation | |
|---|---|
| Interface Type | Single Conversion Mode |
| Bytes to Configure | |
| - before/while busy | 4 |
| - after busy | 1 |
| Bytes to read | Data + Status + CRC |
| Repeat Read Command | False |
| Enable CS between Samples | False |
| SPI Write Buffer U8 | 0x08 |
| 0x28 | |
| 0x00 | |
| 0x60 | |
Figure 10 : Continuous Conversion mode with RDY (ADI7190 example)
| LabVIEW Implementation | |
|---|---|
| Interface Type | Continuous Conversion Mode |
| Bytes to Configure | |
| - before/while busy | 0 |
| - after busy | 1 |
| Bytes to read | Data + Status + CRC |
| Repeat Read Command | True |
| Enable CS between Samples | True |
| SPI Write Buffer U8 | 0x58 |
Figure 11 : Continuous Read Mode with RDY (ADI7190 example)
| LabVIEW implementation | |
|---|---|
| Interface Type | Continuous Read Mode |
| Bytes to Configure | |
| Before/while busy | 1 |
| After Busy | 0 |
| Bytes to Read | Data + Status + CRC |
| Repeat Read Command | False |
| Enable CS between Samples | True |
| SPI Write Buffer U8 | 0x5C |
resources/eval/sdp/sdp-s/peripherals/spi.txt · Last modified: 06 Oct 2011 16:37 by Jean McAdam