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(1) Serial Clock
!
Clock source
SBI0CR1<SCK2 to SCK0> 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. The SCK pin goes High when data transfer starts. 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.
1
SCK pin output
a
SO pin output
0
Write
a
transmitted data
External clock (<SCK2 to SCK0> = "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 MHz (when fc = 16 MHz).
SCK pin
Figure 3.10.24 Maximum data transfer frequency when external clock input used
Automatic wait function
2
3
7
8
a
a
a
a
a
1
2
5
6
7
Figure 3.10.23 Automatic-wait Function
t
t
SCKL
SCKH
t
, t
> 8/fc
SCKL
SCKH
91C824-172
1
2
6
7
8
b
b
b
b
b
b
0
1
4
5
6
7
b
c
TMP91C824
1
2
3
c
c
c
0
1
2
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