UPD784938 Datasheet, PDF (445/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 18 ASYNCHRONOUS SERIAL INTERFACE/3-WIRE SERIAL I/O
(b) LSB-first
Figure 18-12. 3-Wire Serial I/O Mode Timing (2/2)
SCK1^Note
SI1 (input)
SO1 (output)
1 2 34567 8
DI0 DI1 DI2 DI3 DI4 DI5 DI6 DI7
DO0 DO1 DO2 DO3 DO4 DO5 DO6 DO7
INTCSI1
Transfer end
interrupt generation
Start of transfer synchronized with fall of SCK1
Execution of instruction that writes to SIO1, etc.
Note Master CPU: Output
Slave CPU: Input
Remark If the µPD784938 is connected to a 2-wire serial I/O device, a buffer should be connected to the SO1 pin as
shown in Figure 18-13. In the example shown in Figure 18-13, the output level is inverted by the buffer, and
therefore the inverse of the data to be output should be written to SIO1.
In addition, non-connection of the on-chip pull-up resistor should be specified for the P31/SO1 pin.
Figure 18-13. Example of Connection to 2-Wire Serial I/O
µPD784938
2-wire serial I/O device
SCK1
SCK
(Serial clock line)
SI1
SO1
SIO
(Serial data line)
Preliminary User’s Manual U13987EJ1V0UM00
445