Operational States Of Serial I/O Units - Fujitsu MB90480 Series Hardware Manual

18.5.2 Operational States of Serial I/O Units

Four serial I/O states are used, namely, STOP, Halt, SDR R/W Wait, and Transfer.
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Operational states of serial I/O units
❍ STOP State
The shift counter is initialized to SIR=0 at reset or by writing "1" to the STOP bit of SMCS.
To return from the STOP state, set STOP = 0 and STRT= 1 (these bits can be set
simultaneously). Because the STOP bit has a higher priority than the STRT bit, data transfer will
not be executed even when STRT = 1 is set while STOP = 1.
❍ Halt State
When the MODE bit is set to "0", the BUSY and SIR bits of SMCS will become BUSY = 0 and
SIR = 1 after data transfer ends. The counter will then be initialized and set to the Halt state. For
returning from the Halt state, set STRT = 1 to resume data transfer operation.
❍ Serial Data Register R/W Wait State
When the MODE bit of SMCS is "1", serial transfer ends, this will result in BUSY = 0 and SIR =
1 and the serial data register R/W wait state will be entered. If the interrupt enable register is set
to "enable", the applicable block will issue an interrupt signal.
When returning from the R/W wait state, the BUSY becomes BUSY = 1 and data transfer
operation will be resumed as soon as a read or write operation is performed for the serial data
register.
❍ Transfer State
In this state, serial transfer is performed if BUSY = 1. Depending on the setting of the MODE bit,
the Halt or R/W wait state will be entered.
Figure 18.5-1 shows the state transitions during operation. Figure 18.5-2 illustrates the concept
of reading and writing the serial data register.
Figure 18.5-1 State transitions during operation of expanded I/O serial interface
Transfer end
STRT=0, BUSY=0
MODE=0
MODE=0
STOP=0
&
&
STOP=0
STRT=1
&
End
Transfer operation
STRT=1, BUSY=1
CHAPTER 18 EXPANDED I/O SERIAL INTERFACE
STOP=0 & STRT=0
STOP=1
STOP=1
&
STRT=1
MODE = 1 & End & STOP = 0
SDR R/W & MODE=1
Reset
STOP
STRT=0, BUSY=0
STOP=0
STOP=1
Serial data register R/W Wait
STRT=1, BUSY=0
MODE=1
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