Single-Chip Microcontrollers User's Manual

402
CHAPTER 18 SERIAL INTERFACE CHANNEL 1
Start bit switching is realized by switching the bit order write to SIO1. The SIO1 shift order remains unchanged.
Thus, switching between MSB-first and LSB-first must be performed before writing data to SIO1.
(4) Transfer start
Serial transfer is started by setting transfer data to the serial I/O shift register 1 (SIO1) when the following two
conditions are satisfied.
• Serial interface channel 1 operation control bit (CSIE1) = 1
• Internal serial clock is stopped or SCK1 is a high level after 8-bit serial transfer.
Caution If CSIE1 is set to "1" after data write to SIO1, transfer does not start.
Upon termination of 8-bit transfer, serial transfer automatically stops and the interrupt request flag (CSIIF1)
is set.
Figure 18-7. Circuit of Switching in Transfer Bit Order
7
6
Internal Bus
1
0
LSB-first
MSB-first Read/Write Gate
SI1 Serial I/O Shift Register 1 (SIO1)
Read/Write Gate
SO1
SCK1
DQ
SO1 Latch