NEC mPD784225 Series User Manual page 286

CHAPTER 16 ASYNCHRONOUS SERIAL INTERFACE/3-WIRE SERIAL I/O
(b) Communication operation
The 3-wire serial I/O mode performs data transfer in 8-byte units. Data is transmitted and received one byte
at a time in synchronization with the serial clock.
The shift operation of the serial I/O shift register n (SIOn) is performed in synchronization with the falling
edge of the serial clock (SCKn). Transmit data is held in the SOn latch, and is output from the SOn pin. Receive
data input to the SIn pin is latched to SIOn at the rising edge of the SCKn signal.
SIOn operation is automatically stopped when 8-bit transfer ends, and an interrupt request flag (SRIFn) is
set.
Remark n = 1, 2
SCKn
SIn
SOn
SRIFn
Remark n = 1, 2
(c) Transfer start
Serial transfer is started by setting transmit data (or reading) to serial I/O shift register n (SIOn) when the
following two conditions are satisfied.
• SIOn operation control bit (CSIEn) = 1
• Following 8-bit serial transfer, the internal serial clock is stopped, or SCKn is high level
• Transmit/receive mode
When CSIEn = 1 and MODEn = 0, and transfer is started with SIOn write
• Receive-only mode
When CSIEn = 1 and MODEn = 1, and transfer is started with SIOn read.
Caution After data is written to SIOn, transfer will not start even if CSIEn is set to "1".
Serial transfer automatically stops at the end of 8-bit transfer, and the interrupt request flag (SRIFn) is set.
Remark n = 1, 2
286
Figure 16-15. 3-Wire Serial I/O Mode Timing
1 2 3
DI7 DI6 DI5
DO7 DO6 DO5
Transfer start in synchronization with falling edge of SCKn
User's Manual U12697EJ3V0UM
4 5 6
DI4 DI3 DI2
DO4 DO3 DO2
7 8
DI1 DI0
DO1 DO0
Transfer completion