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CHAPTER 22 SERIAL I/O
22.4.2
Serial I/O Operation
There are four serial I/O operation statuses:
• STOP
• Halt
• SDR Read/Write standby
• Transfer
■ Serial I/O Operation
●
STOP
The STOP state is initiated upon RESET or when "1" is written to the STOP bit of SMCS. The shift
counter is initialized, and "0" is written to SIR.
To resume operation from the STOP state, write "0" to STOP and "1" to STRT. (These two bits can be
written to simultaneously.) Since the STOP bit overrides the STRT bit, transfer cannot be started by writing
"1" to STRT while "1" is written to STOP.
●
Halt
When transfer is completed while the MODE bit is "0", "0" is set to BUSY and "1" is set to SIR of the
SMCS, the counter is initialized, and the system stops. To resume operation from the stop state, write "1" to
STRT.
●
Serial data register Read/Write standby
When transfer is completed while the MODE bit is "1", "0" is set to BUSY and "1" is set to SIR of the
SMCS, and the system enters the serial data register Read/Write standby state. If the interrupt enable flag is
set, an interrupt signal is output from this block.
To resume operation from Read/Write standby state, read or write to the serial data register. This sets the
BUSY bit to "1" and starts data transfer.
●
Transfer
"1" is set to the BUSY bit and serial transfer is being performed. According to the MODE bit, the halt state
or Read/Write standby state comes next.
Figure 22.4-1 is a diagram of the operation transitions.
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