HD404654 Datasheet, PDF (75/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404654 Series
Registers for Serial Interface 1
When serial interface 1 operation is selected, serial data is read and written by the following registers.
• Serial mode register 1A (SM1A: $005)
• Serial mode register 1B (SM1B: $028)
• Serial data register 1 (SR1L: $006, SR1U: $007)
• Port mode register A (PMRA: $004)
• Miscellaneous register (MIS: $00C)
Serial Mode Register 1A (SM1A: $005): This register has the following functions (figure 56).
• R4₁/SCK₁ pin function selection
• Serial interface 1 transmit clock selection
• Serial interface 1 prescaler division ratio selection
• Serial interface 1 initialization
Serial mode register 1A is a 4-bit write-only register. It is reset to $0 by MCU reset.
A write signal input to serial mode register 1A (SM1A: $005) discontinues the input of the transmit clock
to serial data register 1 (SR1L: $006, SR1U: $007) and the octal counter, and the octal counter is reset to
000. Therefore, if a write is performed during data transfer, the serial 1 interrupt request flag (IFS1: $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.
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