UPD784938 Datasheet, PDF (458/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 19 3-WIRE SERIAL I/O MODE
19.2 Configuration
Figure 19-1 shows the block diagram of the clocked serial interface in the 3-wire serial I/O mode (note that the functions
of both channels are identical).
Figure 19-1. Clocked Serial Interface Block Diagram
P27/SI0
SIO
Shift
LSB/MSB
To P33/SO0 port block
CSIM
EN SEL DIR CRX MO SEL SEL SEL
CSI ST
E D CL2 CL1 CL0
N-ch open-drain
specification
QS
0
Write to SIO
Read to SIO
1
To P32/SCK0 port block
Serial clock counter
SELCL. 0 to 2
R
Interrupt signal
generation
circuit
Eighth clock
INTCSI
External clock selection
fXX/8
fXX/16
fXX/32
fXX/64
fXX/128
(1) Serial shift register (SIO)
The SIO converts 8-bit serial data to 8-bit parallel data, and vice versa. SIO is used for both transmission and reception.
Data is received or transmitted starting from the MSB (or LSB). Actual transmit/receive operations are controlled by
writing to/reading from SIO.
SIO can be read or written to with an 8-bit manipulation instruction. The contents of SIO are undefined after RESET
input.
(2) 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.
(3) Interrupt signal generator
A interrupt request is generated when 8 serial clocks have been counted by the serial clock counter.
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Preliminary User’s Manual U13987EJ1V0UM00