NEC 78014Y Series, User Manual

Page: 285 / 547

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CHAPTER 15 SERIAL INTERFACE CHANNEL 0 (
µ
PD78014 Subseries)
285
(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 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, a CPU other than those
of 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.
(2) SBI definition
The SBI serial data format and implication of signals to be used are defined as follows.
Serial data to be transferred with SBI is distinguished into three types, “address”, “command” and “data”.
Figure 15-12 shows the address, command and data transfer timings.