CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U15195EJ5V0UD
456
(3) Continuous transmission of 3 or more frames
In addition to the 1-frame/2-frame transmission function, UART1 also enables continuous transmission of 3 or
more frames, using the method shown below.
(a) How to continuously transmit 3 or more frames (when the stop bit is 1 bit (SL bit = 0))
Three frames can be continuously transmitted by writing transmit data to the TXS1/TXSL1 register in the
period between the generation of the transmission completion interrupt request (INTST1) and 4
×
2/f
XX
before the output of the last stop bit.
The INTST1 interrupt becomes high level 2/f
XX
after being output and returns to low level 2/f
XX
later.
TXS1/TXSL1 can only be written after the INTST1 interrupt level has fallen. The time from INTST1
interrupt generation to the completion of transmit data writing (t) is therefore indicated by the following
expression.
t = (Time of one stop bit) – (2
×
2/f
XX
+ 4
×
2/f
XX
)
f
XX
= Internal system clock
Caution 4
×
2/f
XX
has a margin of double the clock that can actually be used for operation.
Example
Count clock frequency = 32 MHz = 32,000,000 Hz
Target baud rate in synchronous mode = 9,600 bps
t = (1/9615.385)
−
( (4 + 8) /32,000,000)
= 104.000
−
0.375
= 103.625 [
µ
s]
Therefore, be sure to write transmit data to TXS1/TXSL1 within 103
µ
s of the generation of the INTST1
interrupt.
Note, however, that because writing to TXS1/TXSL1 may be delayed depending on the priority order of
the interrupt or the interrupt servicing time, be sure to allow sufficient time for writing transmit data after
the INTST1 interrupt has been generated. If there is not enough time for continuous transmission due to
a delay in writing to TXS1/TXSL1, a 1-bit high level is transmitted.
Note also that if the stop bit length is 2 bits (SL = 1), the INTST1 interrupt will be generated when the
second stop bit is output.
Figure 10-19. Continuous Transmission of 3 or More Frames
2/f
XX
2/f
XX
2/f
XX
4
×
2/f
XX
TXS1/TXSL1 write period for 3-frame
continuous transmission
Stop bit
INTST1 interrupt
Содержание PD703114
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