CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
343
Digital Blocks
17.1.11
SPI Protocol Function
The Serial Peripheral Interface (SPI) is a Motorola™ specification for implementing full-duplex synchronous serial communi-
cation between devices. The 3-wire
uses both edges of the clock to enable synchronous communication, without
the need for stringent setup and hold requirements.
shows the basic signals in a simple connection
Figure 17-5. Basic SPI Configuration.
A device can be a master or slave. A master outputs clock
and data to the
and inputs slave data. A slave
device inputs clock and data from the
and
outputs data for input to the master. The master and slave
together are essentially a circular shift register, where the
master is generating the clocking and initiating data trans-
fers.
A basic data transfer occurs when the master sends eight
bits of data, along with eight clocks. In any transfer, both
master and slave are transmitting and receiving simultane-
ously. If the master is only sending data, the received data
from the slave is ignored. If the master wishes to receive
data from the slave, the master must send dummy bytes to
generate the clocking for the slave to send data back.
17.1.11.1
SPI Protocol Signal Definitions
The SPI Protocol signal definitions are located in
The use of the SS_ signal varies according to the capability
of the slave device.
SPI Master
SPI Slave
MOSI
SCLK
SS_
MISO
MOSI
MISO
SCLK
Data is output by both
the Master and Slave, on
one edge of the clock.
Data is registered at the input
of both devices, on the
opposite edge of the clock.
MOSI
SCLK
SS_
MISO
Table 17-8. SPI Protocol Signal Definitions
Name
Function
Description
MOSI
Master Out
Slave In
Master data output.
MISO
Master In
Slave Out
Slave data output.
SCLK
Serial Clock
Clock generated by the master.
SS_
Slave Select
(active low)
This signal is provided to enable multi-slave
connections to the MISO pin. The MOSI and
SCLK pins can be connected to multiple
slaves, and the SS_ input selects which slave
will receive the input data and drive the MISO
line.
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