Bit Sequential Buffer Operation - NEC PD789860 User Manual

12.4 Bit Sequential Buffer Operation

Set as follows to operate the bit sequential buffer.
<1> Set values to bit sequential buffer 10 data registers L and H (BSFRL10, BSFRH10)
<2> Set the bit sequential buffer to operation enabled (BSFE10 = 1)
If the LSB of BSFRL10 is being output at P20/BSFO/TMO, set P20 to output mode (PM20 = 0) and the
output latch of P20 to 0
<3> Start the clock operation
If the clock is input before the bit sequential buffer starts operation, the output time of the start bit may be shorter
than one cycle of the clock when output commences, as shown in the figure below.
Timer 40
match signal
BSFE10
BSFRL10,
BSFRH10
Bit sequential
buffer output
Figure 12-4 shows the operation timing of the bit sequential buffer.
Timer 40
match signal
BSFE10
BSFRL10,
Undefined
BSFRH10
Bit sequential
buffer output
Cautions 1. Even if data is written to the data register while the bit sequential buffer is operating, the
shift clock (timer 40 match signal) will not stop. Data should therefore be written to the
data register when the shift clock is low level.
2. The value of the data register is undefined after a shift.
×: Undefined
Remark
134
CHAPTER 12 BIT SEQUENTIAL BUFFER
t0
5555H
t1< t0
Figure 12-4. Operation Timing of Bit Sequential Buffer
2AAAH
5555H
User's Manual U14826EJ5V0UD
2AAAH 1555H
t2
t1
t2 = t0
1555H 0AAAH
0AAAH
×555H
×2AAH