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

(3) 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 18-7 shows the configuration of the serial I/O shift register 1 (SIO1) 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 6 (DIR) of the serial operating mode register 1
(CSIM1).
7
6
Internal Bus
1
0
LSB-first
MSB-first
SI1
SO1
SCK1
Start bit switching is realized by switching the bit order for data write to SIO1. The SIO1 shift order remains
unchanged.
Thus, switching between MSB-first and LSB-first must be performed before writing data to the 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.
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CHAPTER 18 SERIAL INTERFACE CHANNEL 1
Figure 18-7. Circuit of Switching in Transfer Bit Order
Read/Write Gate
Serial IO Shift Register 1 (SIO1)
Read/Write Gate
SO1 Latch
D Q