NEC uPD78056Y - Manual (Page 288)

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CHAPTER 16 SERIAL INTERFACE CHANNEL 0 (
µ
PD78054 Subseries)
16.1 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 switch the operation mode (3-wire serial I/O, 2-wire serial I/O, SBI) of serial interface
channel 0. Switch the operation mode after stopping 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).
The SBI mode conforms to the NEC serial bus format and transmits/receives transfer data discriminating it
as three types: “address”, “command”, and “data”.
• Address : Data that selects the target device of the serial communication
• Command : Data that gives instruction to the target device
• Data : Data that is actually transmitted
For the actual transmission, the master device outputs “address” on the serial bus and selects the slave device
to be the target of communication from multiple devices. Then, the serial transmission is realized by
transmitting/receiving “command” and “data” between the master device and the slave device. The receive
side automatically discriminates the received data as “address”, “command”, or “data”, by hardware.
This function enables the input/output ports to be used effectively and simplifies the application program to
control serial interface channel 0.
In this mode, the wake-up function for handshake and the output function of acknowledge and busy signals
can also be used.