HD404054 Datasheet, PDF (71/101 Pages) Hitachi Semiconductor – HMCS400-series microcomputers designed to increase program productivity with large-capacity memory

HD404054 Series/HD404094 Series
Registers for Serial Interface
The serial interface operation is selected, and 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 53).
• 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 (SM1A: $005) 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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