CHAPTER 14 SERIAL INTERFACE CHANNEL 0
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(1) Serial I/O shift register 0 (SIO0)
This is an 8-bit register to carry out parallel/serial conversion and to carry out serial transmission/reception
(shift operation) in synchronization with the serial clock.
SIO0 is set with an 8-bit memory manipulation instruction.
When bit 7 (CSIE0) of serial operating mode register 0 (CSIM0) is 1, writing data to SIO0 starts serial
operation.
In transmission, data written to SIO0 is output to the serial output (SO0) or serial data bus (SB0/SB1).
In reception, data is read from the serial input (SI0) or SB0/SB1 to SIO0.
The SBI mode and 2-wire serial I/O mode bus configurations enables the pin to serve for both input and
output. Thus, in the case of a device for reception, write FFH to SIO0 in advance (except when address
reception is carried out by setting bit 5 (WUP) of CSIM0 to 1).
In the SBI mode, the busy state can be cleared by writing data to SIO0. In this case, bit 7 (BSYE) of the
serial bus interface control register (SBIC) is not cleared to 0.
RESET input makes SIO0 undefined.
(2) Slave address register (SVA)
This is an 8-bit register to set the slave address value for connection of a slave device to the serial bus.
SVA is set with an 8-bit memory manipulation instruction. This register is not used in the 3-wire serial I/O
mode.
The master device outputs a slave address for selection of a particular slave device to the connected slave
device. These two data (the slave address output from the master device and the SVA value) are compared
with an address comparator. If they match, the slave device has been selected. In that case, bit 6 (COI)
of serial operating mode register 0 (CSIM0) becomes 1.
Address comparison can also be executed on the data of LSB-masked high-order 7 bits by setting bit 4
(SVAM) of the interrupt timing specify register (SINT) to 1.
If no matching is detected in address reception, bit 2 (RELD) of the serial bus interface control register (SBIC)
is cleared to 0. The wake-up function can be used by setting bit 5 (WUP) of CSIM0 to 1. In this case, the
interrupt request signal (INTCSI0) is generated only when the slave address output by the master coincides
with the value of SVA, and it can be learned by this interrupt request that the master requests for
communication. If bit 5 (SIC) of the interrupt timing specify register (SINT) is set to 1, the wake-up function
cannot be used even if WUP is set to 1 (an interrupt request signal is generated when bus release is
detected). To use the wake-up function, clear SIC to 0.
Further, an error can be detected by using SVA when the device transmits data as master or slave device
in the SBI or 2-wire serial I/O mode.
RESET input makes SVA undefined.
(3) SO0 latch
This latch holds SI0/SB0/P25 and SO0/SB1/P26 pin levels. It can be directly controlled by software.
In the SBI mode, this latch is set upon termination of the 8th serial clock.
(4) Serial clock counter
This counter counts the serial clocks to be output and input during transmission/reception and to check
whether 8-bit data has been transmitted/received.
(5) Serial clock control circuit
This circuit controls serial clock supply to the serial I/O shift register 0 (SIO0). When the internal system
clock is used, the circuit also controls clock output to the SCK0/P27 pin.