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CHAPTER 17 SERIAL INTERFACE CHANNEL 0 (
µ
PD78078 SUBSERIES)
334
(1) SBI functions
In the conventional serial I/O format, when a serial bus is configured by connecting two or more devices,
many ports and wiring are necessary, to provide chip select signal to identify command and data, and to
judge the busy state, because only the data transfer function is available. If these operations are to be
controlled by software, the software must be heavily loaded.
In SBI, a serial bus can be configured with two signal lines of serial clock SCK0 and serial data bus SB0
(SB1). Thus, use of SBI leads to reduction in the number of microcontroller ports and that of wirings and
routings on the board.
The SBI functions are described below.
(a) Address/command/data identify function
Serial data is distinguished into addresses, commands, and data.
(b) Chip select function by address transmission
The master executes slave chip selection by address transmission.
(c) Wake-up function
The slave can easily judge address reception (chip select judgment) with the wake-up function (which
can be set/reset by software).
When the wake-up function is set, the interrupt request signal (INTCSI0) is generated upon reception
of a match address.
Thus, when communication is executed with two or more devices, the CPU except the selected slave
devices can operate regardless of underway serial communications.
(d) Acknowledge signal (ACK) control function
The acknowledge signal to check serial data reception is controlled.
(e) Busy signal (BUSY) control function
The busy signal to report the slave busy state is controlled.