HD404369 Datasheet, PDF (82/117 Pages) Hitachi Semiconductor – 4-bit HMCS400-Series microcomputer

HD404369 Series
Serial Mode Register (SMR: $005): This register has the following functions (figure 62).
• R0₀/SCK pin function selection
• Transmit clock selection
• Prescaler division ratio selection
• Serial interface initialization
Serial mode register (SMR: $005) is a 4-bit write-only register. It is reset to $0 by MCU reset.
A write signal input to serial mode register (SMR: $005) discontinues the input of the transmit clock to the
serial data register and octal counter, and the octal counter is reset to 000. Therefore, if a write is performed
during data transfer, the serial interrupt request flag (IFS: $003, bit 2) is set.
Written data is valid from the second instruction execution cycle after the write operation, so the STS
instruction must be executed at least two cycles after that.
Serial mode register (SMR: $005)
Bit
Initial value
Read/Write
Bit name
3
0
W
SMR3
2
0
W
SMR2
1
0
W
SMR1
0
0
W
SMR0
SMR3
0
1
R0₀/SCK
Mode Selection
R0₀
SCK
SMR2
0
1
SMR1
0
1
0
1
SMR0
0
1
0
1
0
1
0
1
SCK
Prescaler
Clock Source Division Ratio
Output Prescaler
Refer to
table 28
Output System clock —
Input External clock —
Figure 62 Serial Mode Register (SMR)
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