
50
μ
PD17145(A1), 17147(A1), 17149(A1)
15. SERIAL INTERFACE (SIO)
The serial interface of the
μ
PD17149(A1) consists of an 8-bit shift register (SIOSFR), a serial mode register,
and a serial clock counter, and is used to input/output serial data.
15.1 Function of Serial Interface
The serial interface can transmit or receive 8-bit data in synchronization with the clock by using three wires:
serial clock input (SCK), serial data output (SO), and serial data input (SI) pins. This serial interface can connect
various peripheral I/O devices in a mode compatible with the method employed for the
μ
PD7500 series and 75X
series.
(1) Serial clock
Four types of serial clocks, three internal and one external, can be selected. If an internal clock is selected
as the serial clock, the selected clock is automatically output to the P0D
0
/SCK pin.
Table 15-1. Serial Clocks
SIOCK1
SIOCK0
Selected Serial Clock
0
0
External clock from SCK pin
0
1
System clock/16
1
0
System clock/128
1
1
System clock/1024
(2) Transfer operation
Each pin of port 0D (P0D
0
/SCK, P0D
1
/SO, P0D
2
/SI) functions as a serial interface pin when SIOEN is set
to 1. If SIOTS is set to 1 at this time, the serial interface starts its operation in synchronization with the falling
edge of the external or internal clock. If SIOTS is set, IRQSIO is automatically cleared.
Data is transferred starting from the most significant bit of the shift register in synchronization with the rising
edge of the serial clock, and the information on the SI pin is stored to the shift register, starting from the
least significant bit, in synchronization with the rising edge of the serial clock.
When 8-bit data has been completely transferred, SIOTS is automatically cleared, and IRQSIO is set.
Remark
When serial transfer is executed, transfer is started only from the most significant bit of the
contents of the shift register. In other words, transfer cannot be started from the least significant
bit. The status of the SI pin is always loaded to the shift register in synchronization with the rising
edge of the serial clock.