Circuit Of Switching In Transfer Bit Order - NEC PD78052 User Manual

CHAPTER 17 SERIAL INTERFACE CHANNEL 0 ( PD78054Y Subseries)
(4) MSB/LSB switching as the start bit
The 3-wire serial I/O mode enables to select transfer to start from MSB or LSB.
Figure 17-9 shows the configuration of the serial I/O shift register 0 (SIO0) and internal bus. As shown in the
figure, MSB/LSB can be read/written in reverse form.
MSB/LSB switching as the start bit can be specified with bit 2 (CSIM02) of the serial operating mode register
0 (CSIM0).
7
6
Internal Bus
1
0
LSB-first
MSB-first
SI0
SO0
SCK0
Start bit switching is realized by switching the bit order for data write to SIO0. The SIO0 shift order remains
unchanged.
Thus, switching between MSB-first and LSB-first must be performed before writing data to SIO0.
(5) Transfer start
Serial transfer is started by setting transfer data to the serial I/O shift register 0 (SIO0) when the following two
conditions are satisfied.
• Serial interface channel 0 operation control bit (CSIE0) = 1.
• Internal serial clock is stopped or SCK0 is a high level after 8-bit serial transfer.
Caution If CSIE0 is set to "1" after data write to SIO0, transfer does not start.
Upon termination of 8-bit transfer, serial transfer automatically stops and the interrupt request flag (CSIIF0)
is set.
360
Figure 17-9. Circuit of Switching in Transfer Bit Order
Read/Write Gate
Serial I/O Shift Register 0 (SIO0)
Read/Write Gate
SO0 Latch
D Q