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6.2 SPI Interface
When in SPI mode, the serial interface operates in 4-wire or 3-wire depending on the state of the SPI_3WIRE configuration bit,
0x000B[3]. The 4-wire interface consists of a clock input (SCLK), a chip select input (CSb), serial data input (SDI), and serial data
output (SDO). The 3-wire interface combines the SDI and SDO signals into a single bidirectional data pin (SDIO). Note that the SCLK
is not required to be active when CSb is high despite the SCLK shown as being active in the following timing diagrams. Both 4-wire and
3-wire interface connections are shown in the following figure.
To SPI
Host
SDI
SDO
I2C_SEL
SCLK
CSb
SPI_3WIRE = 0
SPI 4-Wire
CSb
SDIO
I2C_SEL
SCLK
SPI_3WIRE = 1
SPI 3-Wire
To SPI
Host
To SPI
Host
Clock IC
Clock IC
Figure 6.6. SPI Interface Connections
Table 6.3. SPI Command Formats
Instruction
I
st
Byte
1
2
nd
Byte 3
rd
Byte Nth Byte
2,3
Set Address 000x xxxx 8-bit Address — —
Write Data 010x xxxx 8-bit Data — —
Read Data 100x xxxx 8-bit Data — —
Write Data + Address In-
crement
011x xxxx 8-bit Data — —
Read Data + Address In-
crement
101x xxxx 8-bit Data — —
Burst Write Data 1110 0000 8-bit Address 8-bit Data 8-bit Data
Note:
1. X = don't care (1 or 0)
2. The Burst Write Command is terminated by de-asserting CSb (CSb = high)
3. There is no limit to the number of data bytes that follow the Burst Write Command, but the address will wrap around to zero in the
byte after address 255 is written.
Writing or reading data consist of sending a “Set Address” command followed by a “Write Data” or “Read Data” command. The 'Write
Data + Address Increment' or “Read Data + Address Increment” commands are available for cases where multiple byte operations in
sequential address locations is necessary. The “Burst Write Data” instruction provides a compact command format for writing data since
it uses a single instruction to define starting address and subsequent data bytes. The first figure below shows an example of writing
three bytes of data using the write commands. This demonstrates that the “Write Burst Data” command is the most efficient method for
writing data to sequential address locations.
Figure 6.8 Example of Reading Three Data Bytes Using the SPI Read Commands on page
61 provides a similar comparison for reading data with the read commands. Note that there is no burst read, only read increment.
Si5386 Rev. E Reference Manual • Serial Interface
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