uPD780065 Subseries PUM - Renesas Electronics

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CHAPTER 16 SERIAL INTERFACE (SIO31)
Notes 1. When CSIE31 = 0 (SIO31 operation stop status), the pins SI31, SO31, and SCK31 can be used for
port functions.
2. When CSIE31 = 1 (SIO31 operation enabled state), the SI31 pin can be used as a port pin if only the
send function is used, and the SO31 pin can be used as a port pin if only the receive-only mode is
used.
Remarks 1. fX: main system clock oscillation frequency
2. Figures in parentheses are for operation with fX = 8.38 MHz.
(2) Communication operations
In the three-wire serial I/O mode, data is transmitted and received in 8-bit units. Each bit of data is sent or received
in synchronization with the serial clock.
The serial I/O shift register 31 (SIO31) is shifted in synchronization with the falling edge of the serial clock.
Transmission data is held in the SO31 latch and is output from the SO31 pin. Data that is received via the SI31
pin in synchronization with the rising edge of the serial clock is latched to SIO31.
Completion of an 8-bit transfer automatically stops operation of SIO31 and sets interrupt request flag (CSIIF31).
SCK31 1
Figure 16-3. Timing of 3-Wire Serial I/O Mode
SI31 DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0
CSIIF31
2 3 4 5 6 7 8
SO31 DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
(3) Transfer start
A serial transfer starts when the following two conditions have been satisfied and transfer data has been set (or
read) to serial I/O shift register 31 (SIO31).
• The SIO31 operation control bit (CSIE31) = 1
• After an 8-bit serial transfer, either the internal serial clock is stopped or SCK31 is set to high level.
• Transmit/transmit and receive mode
When CSIE31 = 1 and MODE1 = 0, transfer starts when writing to SIO31.
• Receive-only mode
When CSIE31 = 1 and MODE1 = 1, transfer starts when reading from SIO31.
Caution After data has been written to SIO31, transfer will not start even if the CSIE31 bit value is set
to “1”.
Completion of an 8-bit transfer automatically stops the serial transfer operation and interrupt request flag
(CSIIF31) is set.
Preliminary User’s Manual U13420EJ2V0UM00
Transfer completion
Transfer starts in synchronization with the SCK31 falling edge