NEC switch User Manual
Page 161
CHAPTER 9 SERIAL INTERFACE 10
User’s Manual U12978EJ3V0UD
161
(2) Communication operation
In the 3-wire serial I/O mode, data transmission/reception is performed in 8-bit units. Data is
transmitted/received bit by bit in synchronization with the serial clock.
Transmit/receive shift register 10 (SIO10) shift operations are performed in synchronization with the fall of the
serial clock (SCK10). Then transmit data is held in the SO10 latch and output from the SO10 pin. Also, receive
data input to the SI10 pin is latched in the input bits of SIO10 on the rise of SCK10.
At the end of an 8-bit transfer, the operation of SIO10 stops automatically, and the interrupt request signal
(INTCSI10) is generated.
Figure 9-3. 3-Wire Serial I/O Mode Timing
1
2
3
4
5
6
7
8
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
End of transfer
Transfer start at the falling edge of SCK10
SCK10
SI10
SO10
INTCSI10
Cautions
1. When data is written to SIO10 in the serial operation disabled status (CSIE10 = 0), the
data cannot be transmitted or received.
2. When data is written to SIO10 in the serial operation disabled status (CSIE10 = 0) and
then serial operation is enabled (CSIE10 = 1), the data cannot be transmitted or
received.
3. Once data has been written to SIO10 with the serial clock selected (CSCK10 = 0),
overwriting the data does not update the contents of SIO10.
4. When CSIM10 is operated during data transmission/reception, data cannot be
transmitted or received normally.
5. When SIO10 is operated during data transmission/reception, the data cannot be
transmitted or received normally.
(3) Transfer start
Serial transfer is started by setting transfer data to transmit/receive shift register 10 (SIO10) when the following
two conditions are satisfied.
• Bit 7 (CSIE10) of serial operation mode register 10 (CSIM10) = 1
• Internal serial clock is stopped or SCK10 is high level after 8-bit serial transfer.
Termination of 8-bit transfer stops the serial transfer automatically and generates the interrupt request signal
(INTCSI10).