Renesas 4514 - Manual (Page 143)

APPLICATION
2.4 Serial I/O
2-40 4513/4514 Group User’s Manual
2.4 Serial I/O
The 4513/4514 Group has a clock-synchronous serial I/O which can be used to transmit and receive 8-bit
data.
This section describes serial I/O functions, related registers, application examples using serial I/O and
notes.
2.4.1 Carrier functions
Serial I/O consists of the serial I/O register SI, serial I/O mode register J1, serial I/O transmit/receive
completion flag SIOF and serial I/O counter.
A clock-synchronous serial I/O uses the shift clock generated by the clock control circuit as a synchronous
clock. Accordingly, the data transmit and receive operations are synchronized with this shift clock.
In transmit operation, data is transmitted bit by bit from the S
OUT pin synchronously with the falling edges
of the shift clock.
In receive operation, data is received bit by bit from the S
IN pin synchronously with the rising edges of the
shift clock.
Note: 4513/4514 Group only supports LSB-first transmission and reception.
■ Shift clock
When using the internal clock of 4513/4514 Group as a synchronous clock, eight shift clock pulses
are output from the S
CK pin when a transfer operation is started. Also, when using some external
clock as a synchronous clock, the clock that is input from the S CK pin is used as the shift clock.
■ Data transfer rate (baudrate)
When using the internal clock, the data transfer rate can be determined by selecting the instruction
clock divided by 4 or 8.
When using an external clock, the clock frequency input to the S
CK pin determines the data transfer
rate.
Figure 2.4.1 shows the serial I/O block diagram.
Fig. 2.4.1 Serial I/O block diagram
J1 2
SIOF
J1 2 J1 1 J1 0
J1 1 J1 0
MSB
1/4
1/8
1
0
P2 1 /S OUT
P2 2 /S IN
P2 0 /S CK
TSIAB TABSI
S OUT
S IN
S CK
J1 3
MR 3
1
0 X IN
Division circuit
(divided by 2)
Internal clock
generation circuit
(divided by 3)
Instruction clock
Serial I/O mode register J1
Serial I/O interrupt Serial I/O counter (3)
Synchronous
circuit
Register B (4) Register A (4)
Serial I/O register SI (8) LSB
Note: The output structure of S CK and S OUT pins is N-channel open-drain.