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CHAPTER 15 SERIAL INTERFACE CHANNEL 0 (
μ
PD78018F SUBSERIES)
(1) Function of SBI
With the existing serial I/O method, many ports and wirings are necessary to identify a chip select signal,
command, data, and busy status when a serial bus consists of plural devices because only a data transfer
function is provided. To perform this control by software, the work load of the software increases.
SBI can constitute a serial bus by using two signal lines: serial clock SCK0 and serial data bus SB0 (SB1).
Therefore, the number of ports of the microcomputer and the wiring length on the printed wiring board can
be reduced effectively.
SBI has the following functions:
(a) Address/command/data identification function
Serial data is identified as an address, a command, or data.
(b) Chip select status by address
The master selects a slave chip by transferring an address to the slave.
(c) Wake-up function
The slave can easily judge that it has received an address (chip select judgement), by using the wake-
up function (which can be set or released by software).
When the wake-up function is set, an interrupt request signal (INTCSI0) is generated when the slave
receives an address that matches the address of the slave.
Therefore, even when the master communicates with two or more devices, the CPU of the slaves other
than that selected can operate regardless of serial communication.
(d) Acknowledge signal (ACK) control function
An acknowledge signal is controlled to check reception of serial data.
(e) Busy signal (BUSY) control function
A busy signal that indicates the busy status of the slave is controlled.