HD404618 Datasheet, PDF (53/91 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404618 Series
Serial Interface
The MCU has a clock-synchronous serial interface which transmits and receives 8-bit data.
The serial interface consists of a serial data register (SR), serial mode register (SMR), port mode register A
(PMRA), octal counter, and multiplexers (see figure 30). The R0₀/SCK pin and the transmit clock are
controlled by writing to the SMR. The transmit clock shifts the contents of the SR, which can be read and
written to by software.
The serial interface is activated by the STS instruction. The octal counter is reset to 000 by this instruction,
starts counting at the falling edge of the transmit clock (SCK), and it increments at the rising edge of the
clock. A serial interrupt request flag is set when the eighth transmit clock signal is input (the serial
interface is reset) or when serial transmission is discontinued (the octal counter is reset).
SO
SCK
SI
I/O
control
logic
I/O
control
logic
Octal
counter (OC)
Serial interrupt
request flag
(IFS)
Clock
1/2
Serial data
register (SR)
Transfer
control
signal
Selector
3
System ^fcyc^/fsub
clock
(t_cyc/t_subcyc)
Prescaler S (PSS)
Serial mode
register
(SMR)
Port mode
register A
(PMRA)
Figure 30 Serial Interface Block Diagram
Serial Mode Register (SMR: $005): Four-bit write-only register that controls the R0₀/SCK pin, prescaler
division ratio, and transmit clock source (table 25 and figure 31). Writing to this register initializes the
serial interface.
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