280
CHAPTER 16 SERIAL INTERFACE CHANNEL 0 (
μ
PD780058 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 change the operating mode (3-wire serial I/O, 2-wire serial I/O, or SBI) while serial interface
channel 0 is enabled to operate. To change the operating mode, once 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) (refer to
Figure 16-1
).
The SBI mode conforms to the NEC serial bus format, and transmits or receives three types of transfer data:
“addresses”, “commands”, “data”.
Address:
Command: Data to give an instruction to the target device
Data:
Data actually transferred
Data to select the target device for serial communication
Actually, the master device outputs an “address” to the serial bus to select one of the slave devices with which
the master device is to communicate. After that, “commands” and “data” are transmitted or received between
the master and slave devices (this is the serial transfer). The receiver can automatically identify the received
data as an “address”, “command”, or “data” by 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.