R01UH0823EJ0100 Rev.1.00
Page 998 of 1823
Jul 31, 2019
RX23W Group
33. Serial Communications Interface (SCIg, SCIh)
ACS0 Bit (Asynchronous Mode Clock Source Select)
Selects the clock source in the asynchronous mode.
The ACS0 bit is valid in asynchronous mode (SMR.CM bit = 0) and when an external clock input is selected
(SCR.CKE[1:0] bits = 10b or 11b). This bit is used to select an external clock input or the logical AND of compare
matches output from the internal TMR.
Set the ACS0 bit to 0 in other than asynchronous mode.
For SCI5 and SCI12, the TMOn output (n = 0, 1) of TMR unit 0 can be set as the base clock source. Refer to
for details.
The ACS0 bits for SCI1 and SCI8 are reserved. The write values to these bits for SCI1 and SCI8 should be 0.
shows a setting example of when TMO0 and TMO1 in the TMR unit 0 are selected for output.
Figure 33.4
Example of Average Transfer Rate Setting When TMR Clock is Input
Table 33.25
Correspondence between SCI Channels and Compare Match Outputs
SCI
TMR
Compare Match Output
SCI5
Unit 0
TMO0, TMO1
SCI12
Unit 0
TMO0, TMO1
1 bit = Base clock x 16
Average transfer rate = 3 MHz/16 = 187.5 kbps
SCK5 base clock
= 4 MHz x 3/4
= 3 MHz (average)
Clock source
TMO0 output
4 MHz
Clock enable
TMO1 output
Clock source
Clock enable
TMO0
TMO1
TMR (unit 0)
0
1
2
3
3
3
3
3
0
1
2
3
0
1
2
1
2
3
1
2
3
1
2
3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
4
5
3
4 MHz
3 MHz
0
1
2
1
2
3
0
1
2
1
2
3
0
1
2
1
2
3
0
1
2
1
2
3
SCI5
SCK5
This figure shows an example when TMR clock is input to SCI5.
When generating 187.5 kbps of TMR average transfer rate for PCLK = 32 MHz:
(1)
Generate a frequency of 4 MHz using TMO0 as the clock source.
(2)
Set TMO1 in the compare match count of TCNT in TMR0 and generate 3/4 clock enable to set
an average transfer rate of 3 MHz/16 = 187.5 kbps.
Setting examples of TMR and SCI
● TMR0.TCR = 08h (TMR0.TCNT is cleared at compare match in TMR0.TCORA, the count is incremented at rising edge of PCLK/2)
● TMR0.TCCR = 09h
● TMR1.TCR = 08h (TMR1.TCNT is cleared at compare match in TMR1.TCORA, the count is incremented at compare match A in TMR0.TCNT)
● TMR1.TCCR = 18h
● TMR0.TCSR = 09h (0 is output at compare match in TMR0.TCORA, 1 is output at compare match in TMR0.TCORB)
● TMR1.TCSR = 09h (0 is output at compare match in TMR1.TCORA, 1 is output at compare match in TMR1.TCORB)
● TMR0.TCNT = TMR1.TCNT = 0
● TMR0.TCORA = 03h, TMR0.TCORB = 01h
● TMR1.TCORA = 03h, TMR1.TCORB = 00h
● SCR.SCK[1:0] = 10b (External clock input or TMR clock input is selected)
● SEMR = 01h (TMR clock input is selected with 16 base clock cycles for 1-bit period)
