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CHAPTER 13 SERIAL INTERFACE CHANNEL 0
13.1 Serial Interface Channel 0 Functions
Serial interface channel 0 employs the following four modes.
Operation stop mode
3-wire serial I/O mode
SBI (serial bus interface) mode
2-wire serial I/O mode
Caution
Do not change the operation mode (3-wire serial I/O, 2-wire serial I/O, or SBI) while the operation
of serial interface channel 0 is enabled. To change the operation mode, stop the serial operation.
(1) Operation stop mode
This mode is used when serial transfer is not carried out. Power consumption can be reduced.
(2) 3-wire serial I/O mode (MSB-/LSB-first selectable)
This mode is used for 8-bit data transfer using three lines, one each for serial clock (SCK0), serial output (SO0)
and serial input (SI0). This mode enables simultaneous transmission/reception and therefore reduces the data
transfer processing time.
The start bit of transferred 8-bit data is switchable between MSB and LSB, so that devices can be connected
regardless of their start bit recognition.
This mode should be used when connecting with peripheral I/O devices or display controllers which incorporate
a conventional synchronous clocked serial interface as is the case with the 75X/XL, 78K, and 17K series.
(3) SBI (serial bus interface) mode (MSB-first)
This mode is used for 8-bit data transfer with two or more devices using two lines of serial clock (SCK0) and
serial data bus (SB0 or SB1).
In the SBI mode, transfer data is classified into “addresses”, “commands”, and “data” in conformance with NEC
serial bus format, and is transmitted or received.
Address
Command : Data that gives direction to target device
Data
: Data actually transferred
: Data to select target device for serial communication
Actual transfer takes place when the master device outputs an “address” onto the serial bus to select a slave
device from multiple devices with which the master is to communicate. “Commands” and “data” are then
transmitted between the master and selected slave device. In this way, serial communication is implemented.
The receiver can automatically identify the received data as “address”, “command”, or “data in hardware.
This function enables the input/output ports to be used effectively and the application program serial interface
control portions to be simplified.
In this mode, the wake-up function for handshake and the output function of acknowledge and busy signals
can also be used.