E202075_HD404889 Datasheet, PDF (122/202 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip LCD Circuit

HD404889/HD404899/HD404878/HD404868 Series
Serial Interface Registers
Serial interface operation setting and serial data reading/writing is controlled by the following registers.
Serial mode register 1 (SMR1: $024)
Serial mode register 2 (SMR2: $025)
Serial data register (SRL: $026, SRU: $027)
Port mode register 3 (PMR3: $00B)
Module standby register 2 (MSR2: $00E)
Serial mode register 1 (SMR1: $024):
Serial mode register 1 (SMR1) has the following functions. See figure 66.
• Serial clock selection
• Prescaler division ratio selection
• Serial interface initialization
The serial mode register 1 (SMR1) is a 4-bit write-only register, and is reset to $0 by an MCU reset.
A write to serial mode register 1 (SMR1) halts the supply of the serial clock to the serial data register (SRL,
SRU) and the octal counter, and resets the octal counter to 000. Therefore, if serial mode register 1
(SMR1) is written to during serial interface operation, data transmission/reception will be suspended and
the serial interrupt request flag (IFS) will be set.
A modification of serial mode register 1 (SMR1) becomes effective after execution of two instructions
following the serial mode register 1 (SMR1) write instruction. The program must therefore provide for the
STS instruction to be executed two cycles after the instruction that writes to serial mode register 1 (SMR1).
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