
CHAPTER 14 SERIAL INTERFACE CHANNEL 0
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(1) SBI functions
In the conventional serial I/O method, when a serial bus is constructed by connecting two or more devices,
many ports and wiring are necessary to distinguish chip select signals and command/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 constructed with two signal conductors of serial clock SCK0 and serial data bus
SB0 (SB1). Thus, SBI is effective to decrease the number of microcomputer 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.
Figure 14-10. Slave Selection with Address
Master
Slave 1
Non-selection
Slave 2
Selection
Slave 3
Non-selection
Slave 4
Non-selection
Slave 2
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 (CSIIF0) 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 serial communication.
(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.