NEC PD75402A - Manual (Page 104)

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CHAPTER 5. PERIPHERAL HARDWARE FUNCTIONS
5.5.6 SBI Mode Operation
The SBI (serial bus interface) is a high-speed serial interface which conforms to the the NEC serial bus format.
The SBI is a single-master high-speed serial bus. Its format includes the addition of bus configuration functions
to the clocked serial I/O method to enable communication to be performed with multiple devices using two signal
lines. Consequently, when a serial bus is configured with multiple microcomputers and peripheral ICs, it is possible
to reduce the number of ports used and the amount of wiring on the substrate.
The master can output to a slave on the serial data bus an address to select the target device for serial
communication, a command which gives a directive to the target device, and actual data. The slave can determine
by hardware whether the received data is an address, command or actual data. This function allows the serial
interface control portion of the application program to be simplified.
SBI functions are incorporated in a number of devices including the 75X series, and 78K series 8-bit single-chip
microcomputers.
An example of a serial bus configuration when CPUs and peripheral ICs with a serial interface conforming to the
SBI are used is shown in Fig. 5-32.
In the SBI the SB0 serial data bus pin is an open-drain output and thus the serial data bus line is in the wired-
OR state. The serial data bus line requires a pull-up resistor.
Fig. 5-32 Example of SBI Serial Bus System Configuration
Master
CPU
SB0
SCK
Seroal Data Bis
Serial Clock
SB0
SCK
Slave CPU
Address 1
SB0
SCK
Slave CPU
Address 2
• • • • • •
SB0
SCK
Slave IC
Address N
+ V DD
Note When master/slave exchange processing is performed, since serial clock line (SCK) input/output switching
is performed asynchronously between master and slave, a pull-up resistor is also required for the serial
clock line (SCK).