FUJITSU MB91F109 FR30 - Manual (Page 273)

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10.2 Serial Mode Register (SMR)
[bit 1] SCKE (SCLK Enable)
When communication is performed in CLK synchronous mode (mode 2), this bit specifies
whether to use the SC pin as a clock input pin or a clock output pin.
Set this bit to "0" in CLK asynchronous mode or external clock mode.
0: Clock input pin (initial value)
1: Clock output pin
To use the SC pin as a clock input pin, set the CS0 bit in advance to 1 to select the external
clock.
[bit 0] SOE (Serial Output Enable)
There is an external pin (SO) that is also designed to be used for a general-purpose I/O port
pin. This bit specifies whether to use the external pin (SO) as a serial output pin or an I/O
port pin.
0: General-purpose I/O port pin (initial value)
1: Serial data output pin (SO)