NEC uPD78056Y - Manual (Page 396)

396
CHAPTER 18 SERIAL INTERFACE CHANNEL 1
(1) Serial I/O shift register 1 (SIO1)
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.
SIO1 is set with an 8-bit memory manipulation instruction.
When the value in bit 7 (CSIE1) of serial operating mode register 1 (CSIM1) is 1, writing data to SIO1 starts
serial operation.
In transmission, data written to SIO1 is output to the serial output (SO1). In reception, data is read from the
serial input (SI1) to SIO1.
RESET input makes SIO1 undefined.
Caution Do not write data to SIO1 while the automatic transmit/receive function is activated.
(2) Automatic data transmit/receive address pointer (ADTP)
This register stores value of (the number of transmit data bytes-1) while the automatic transmit/receive function
is activated. As data is transferred/received, it is automatically decremented.
ADTP is set with an 8-bit memory manipulation instruction. The high-order 3 bits must be set to 0.
RESET input sets ADTP to 00H.
Caution Do not write data to ADTP while the automatic transmit/receive function is activated.
(3) Serial clock counter
This counter counts the serial clocks to be output and input during transmission/reception to check whether
8-bit data has been transmitted/received.