NEC PD17062 - Manual (Page 212)

212
µ
PD17062
16.4.2 SIO0NWT (Serial I/O No-Wait) Flag
Writing appropriate data into the SIO0NWT flag can both release wait and execute forced wait.
(1) Writing 0 into SIO0NWT
In this case, forced wait is executed. In other words, the clock being supplied to the clock counter and
presettable shift register is disabled.
If the SIO0MS flag of the serial interface mode register is set to 1 at this time, shift clock operation stops
in the current state.
(2) Writing 1 into SIO0NWT
In this case, wait is released. In other words, the clock being supplied to the clock counter and presettable
shift register is enabled. If the SIO0MS flag of the serial interface mode register is set to 1 at this time,
the shift clock operation resumes from the state existing immediately before waiting began.
16.4.3 SBACK (Serial Bus Acknowledge)
The operation of SBACK varies with the operation mode of the serial interface.
The following describes the operation of SBACK.
(1) For reception in two-wire bus mode (SIO0TX = 0)
In this case, the data set in the SBACK flag is automatically output to the SDA pin at the acknowledge output
timing. The contents of the SBACK flag can be changed only by executing POKE instruction on the wait
register. For this reason, to return acknowledgement continuously, simply write 0 into the SBACK flag.
Then, 0 is automatically transmitted as an acknowledgement. This eliminates the need to manipulate the
SBACK flag each time 1-byte data is received.
Data must be written to the SBACK flag after the 9th bit of the data has been set but before the 9th bit
of the next data is set. Normally, wait is instigated at the falling edge of the 8th or 9th bit. Therefore,
data should be written into the SBACK flag at this time.
Fig. 16-5 Timing of SBACK Rewriting during Wait
5 6 7 8 9
SCL
Clock counter
SDA
SBACK=1 SBACK=0
SBACK
←
0
SIO0NWT
←
1
Wait