UPD72042BGT NEC [NEC], UPD72042BGT Datasheet - Page 22

• Manufacturer Part Number: UPD72042BGT
• Description: LSI DEVICE FOR Inter Equipment Bus (IEBus) PROTOCOL CONTROL
• Manufacturer: NEC [NEC]

3. MICROCOMPUTER INTERFACE
3.1 TRANSFER METHOD
mode.
pin (pin 12). (See Section 3.3 for details.)
(1) Three-wire serial I/O (SEL
(2) Two-wire serial I/O (SEL
22
Either of two microcomputer interface modes can be selected: three-wire serial I/O mode or two-wire serial I/O
Whether three-wire serial I/O mode or two-wire serial I/O mode is selected depends on the input level of the SEL
SEL
SEL
Notes 1. The SI pin for three-wire serial I/O mode is also used as the SIO pin for two-wire serial I/O mode.
Three wires are used to read and write data. The three wires are the serial clock input (SCK), serial data input
(SI
(a) Read operation
(b) Write operation
Two wires are used to read and write data. The two wires are the serial clock input (SCK) and serial data I/O
(SIO
(a) Read operation
(b) Write operation
Note 1
Data is output to the SO pin upon detecting the falling edge of the SCK pin.
Data is input via the SI pin upon detecting the rising edge of the SCK pin. At this time, 1 is output on the
SO pin.
The SIO pin is placed in the output state, and data is output upon detecting the falling edge of the SCK pin.
The SIO pin is placed in the input state, and data is input upon detecting the rising edge of the SCK pin.
Note 1
2. The impedance of the SO pin for three-wire serial I/O mode goes high in two-wire serial I/O mode. So,
1: Three-wire serial I/O
0: Two-wire serial I/O
), and serial data output (SO
connect the SO pin to GND or V
).
0)
1)
Note 2
Data Sheet S13990EJ3V0DS
DD
).
.
PD72042B