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Serial Host Interface
SHI Programming Considerations
S
Slave Address
Start
Bit
Figure 9-11 I
Note:
The first data byte in a write-bus cycle can be used as a user-predefined control
byte (e.g., to determine the location to which the forthcoming data bytes should be
transferred).
9.7
SHI PROGRAMMING CONSIDERATIONS
The SHI implements both SPI and I
slave device or a single-master device. Once the operating mode is selected, the SHI may
communicate with an external device by receiving and/or transmitting data. Before changing
the SHI operational mode, an SHI individual reset should be generated by clearing the HEN
bit. The following paragraphs describe programming considerations for each operational
mode.
9.7.1
SPI SLAVE MODE
The SPI slave mode is entered by enabling the SHI (HEN=1), selecting the SPI mode
2
(HI
C=0), and selecting the slave mode of operation (HMST=0). The programmer should
verify that the CPHA and CPOL bits (in the HCKR) correspond to the external host clock
phase and polarity. Other HCKR bits are ignored. When configured in the SPI slave mode, the
SHI external pins operate as follows:
•
SCK/SCL is the SCK serial clock input.
•
MISO/SDA is the MISO serial data output.
•
MOSI/HA0 is the MOSI serial data input.
•
SS/HA2 is the SS slave select input.
9-22
ACK from
Slave Device
1
A
Data Byte
N = 0 to M
Data Bytes
R/W
2
C Bus Protocol For Host Read Cycle
2
C bus protocols and can be programmed to operate as a
DSP56367
ACK from
Master Device
from Master Device
A
Last Data Byte
AA0426
No ACK
1
P
Stop
Bit
MOTOROLA
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