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(1) Serial Clock
1.
Clock source
SBI0CR1<SCK2:0> is used to select the following functions:
Internal clock
In internal clock mode one of seven frequencies can be selected. The serial clock
signal is output to the outside on the SCK pin.
When the device is writing (in transmit mode) or reading (in receive mode), data
cannot follow the serial clock rate, so an automatic wait function is executed
which automatically stops the serial clock and holds the next shift operation until
reading or writing has been completed.
SCK pin output
1
a
SO pin output
0
Writing
a
transmission
data
Figure 3.10.22 Automatic Wait Function
External clock (<SCK2:0> = "111")
An external clock input via the SCK pin is used as the serial clock. In order to
ensure the integrity of shift operations, both the high and low-level serial clock
pulse widths shown below must be maintained. The maximum data transfer
frequency is 1.25 MHz (when f
SCK pin
Figure 3.10.23 Maximum Data Transfer Frequency when External Clock Input
Automatic wait
2
3
7
8
a
a
a
a
a
1
2
5
6
7
= 20 MHz).
SYS
t
t
SCKL
SCKH
t
t
> 8 f
SCKL and
SCKH
SYS
92CM22-192
1
2
6
7
8
1
b
b
b
b
b
b
c
0
1
4
5
6
7
0
b
c
TMP92CM22
2
3
c
c
1
2
2007-02-16
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