FUJITSU Semiconductor Controller MB89950/950A - Manual (Page 203)

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CHAPTER 9 8-BIT SERIAL I/O
9.9 Connection Example for 8-bit Serial I/O
This section shows an example of connecting together two MB89950/950A series 8-bit
serial I/O and performing bi-directional serial I/O.
■ Bi-directional serial I/O performing
Figure 9.9-1 Connection example for 8-bit serial I/O (interface between two MB89950/950A)
Figure 9.9-2 Operation of bi-directional serial I/O
SI
SO
SCK
SO
SI
SCK
SIO-A SIO-B
Output Input
Internal shift clock External shift clock
SI
SO
SCK
SO
SI
SCK
SIO-A SIO-B
Output Input
Internal shift clock External shift clock
SIO-A
START START
SIO-B
NO
YES
SIO-A
YES (SST="0")
NO
YES
NO
END
YES (SST="0")
NO
SIO-B
Halt operation SIO-A
(SST = "0")
Set the SI pin as serial
data input (input port).
- Set the SCK pin as the shift clock output
- Set the SO pin as the serial data output
- Select an internal shift clock
- Set the data transfer (shift) direction - Set the SCK pin as the shift clock output
- Set the SO pin as the serial data output
- Select an internal shift clock
- Select the same data transfer (shift)
direction as SIO-A
Is serial transfer
enabled on SIO-B? *1
Set output data
Start serial transfer*2
(SST = "1")
Serial data transfer
in progress
Have 8 bits been transferred? *3
Read input data
More data to send?
Transfer enable state
SIO-A outputs serial data
... Simultaneously, SIO-B inputs serial data
Halt operation SIO-B
(SST = "0")
Set the SI pin as serial
data input (input port).
Enable serial transfer
(SST = "1")
Set output data
Serial data transfer
in progress
Have 8 bits been transferred? *3
Read input data
SST: The SST bit is the serial I/O transfer start bit in the serial mode register (SMR).
*1: If the SO, SI, and SCK pins only are connected, there is no direct method of confirming whether
SIO-B has enabled serial transfer. Therefore, SIO-A must use a software timer or similar to delay
time for a sufficient time for SIO-B to enable serial transfer.
*2: Data is not transferred correctly if SIO-A starts data transfer when SIO-B has not enabled
serial transfer.
*3. An interrupt request is generated after 8-bit data have been transferred.