NEC PD750008 - Manual (Page 143)

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CHAPTER 5 PERIPHERAL HARDWARE FUNCTIONS
5.6 SERIAL INTERFACE
5.6.1 Serial Interface Functions
The µPD750008 contains a clock synchronous 8-bit serial interface, which has four modes.
The functions of the four modes are outlined below.
(1) Operation halt mode
This mode is used when serial transfer is not performed. This mode reduces power consumption.
(2) Three-wire serial I/O mode
In this mode, 8-bit data is transferred through three lines: Serial clock (SCK), serial output (SO), and serial
input (SI).
The three-wire serial I/O mode allows full-duplex transmission, so data transfer can be performed at higher
speed.
The user can choose 8-bit data transfer starting with the MSB or LSB, so devices starting with either the
MSB or LSB can be connected.
The three-wire serial I/O mode enables connections to be made with the 75XL series, 78K series, and
many other types of peripheral I/O devices.
(3) Two-wire serial I/O mode
In this mode, 8-bit data is transferred through two lines: Serial clock (SCK) and serial data bus (SB0 or
SB1). By controlling output levels on the two lines by software, communication with multiple devices is
enabled.
The output levels of SCK and SB0 (or SB1) can be controlled by software, so the user can match an
arbitrary transfer format. This means that a line that has been required for handshaking to connect multiple
lines can be eliminated for more efficient input/output port utilization.
(4) Serial bus interface (SBI) mode
In this mode, communication with multiple devices can be performed using two lines: Serial clock (SCK)
and serial data bus (SB0 or SB1).
This mode conforms to the NEC serial bus format.
In this mode, the transmitter can output, on the serial data bus, an address for selecting a device subject
to serial communication, commands directed to the remote device, and data.
The receiver can identify an address, commands, and data from received data by hardware. This function
enables more efficient input/output port utilization as in the case of the two-wire serial I/O mode. In
addition, this function can simplify the serial interface control portion of an application program.