UPD784938 Datasheet, PDF (442/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 18 ASYNCHRONOUS SERIAL INTERFACE/3-WIRE SERIAL I/O
(1) Serial shift register (SIO1/SIO2)
SIO1 and SIO2 convert 8-bit serial data to 8-bit parallel data, and vice versa. SIO1/SIO2 is used for both transmission
and reception.
Actual transmit/receive operations are controlled by writing to/reading from SIO1/SIO2.
These registers can be read or written with an 8-bit manipulation instruction.
The contents of SIO1/SIO2 are undefined after RESET input.
(2) SO latch
The SO latch holds the SO1/SO2 pin output level.
(3) Serial clock selector (1/2n)
Generates and selects the serial clock to be used.
(4) Serial clock counter
Counts the serial clocks output or input in a transmit/receive operation, and checks that 8-bit data transmission/reception
has been performed.
(5) Interrupt signal generator
Generates an interrupt request when 8 serial clocks have been counted by the serial clock counter.
(6) Selector
Selects whether data is input to the serial shift registers 1 and 2 (SIO1 and SIO2) from the SI1 and SI2 pins or output
latches.
(7) Direction control circuit
Switches between MSB-first and LSB-first modes.
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Preliminary User’s Manual U13987EJ1V0UM00