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Page 98
13. Timer A
p
u
o
r
G
0
8
/
C
6
1
M
Item
Specification
Count source
External signals input to TAiIN pin (effective edge can be selected by software)
TB2 overflows or underflows, TAj overflows or underflows
Count operation
Up count or down count can be selected by external signal or software
When the timer overflows or underflows, it reloads the reload register con
tents before continuing counting (Note)
Divide ratio
1/ (FFFF16 - n + 1) for up count
1/ (n + 1) for down count
n : Set value
Count start condition
Count start flag is set (= 1)
Count stop condition
Count start flag is reset (= 0)
Interrupt request generation timing The timer overflows or underflows
TAiIN pin function
Programmable I/O port or count source input
TAiOUT pin function
Programmable I/O port, pulse output, or up/down count select input (Setting by
the corresponding function select registers A and B)
Read from timer
Count value can be read out by reading timer Ai register
Write to timer
When not counting
Value written to timer Ai register is written to both reload register and counter
When counting
Value written to timer Ai register is written to only reload register
(Transferred to counter at next reload time)
Select function
Free-run count function
Even when the timer overflows or underflows, the reload register content is
not reloaded to it
Pulse output function
Each time the timer overflows or underflows, the TAiOUT pin’s polarity is reversed
(2) Event counter mode
In this mode, the timer counts an external signal or an internal timer’s overflow. Timers A0 and A1 can count a single-
phase external signal. Timers A2, A3, and A4 can count a single-phase and a two-phase external signal. Table
13.2
lists timer specifications when counting a single-phase external signal. Figure 1
3.6 shows the timer Ai mode register
in event counter mode.
Table 13.3 lists timer specifications when counting a two-phase external signal.
Figure 13.7 shows the timer Ai mode register in event counter mode.
Table 13.2 Timer specifications in event counter mode (when not processing two-phase pulse signal)
Figure 13.6 Timer Ai mode register in event counter mode
Note 1: This bit is valid when only counting an external signal.
Note 2: Set the corresponding function select register A to I/O port, and port direction
register to “0”.
Timer Ai mode register
(When not using two-phase pulse signal processing)
b7
b6
b5
b4
b3
b2
b1
b0
Operation mode select bit
0 1 : Event counter mode
b1 b0
TMOD1
TMOD0
MR0
Count polarity
select bit (Note 1)
MR2
MR1
MR3
0 : (Set to “0” in event counter mode)
TCK1
TCK0
01
0
0 : Counts external signal's falling edges
1 : Counts external signal's rising edges
Up/down switching
cause select bit
0 : Up/down flag's content
1 : TAiOUT pin's input signal (Note 2)
Bit symbol
Bit name
Function
W
R
Count operation type
select bit
Two-phase pulse signal
processing operation
select bit
0 : Reload type
1 : Free-run type
When not using two-phase pulse signal
processing, set this bit to “0”
Symbol
Address
When reset
TAiMR(i=0 to 4)
035616 to 035A16 00000X002
This bit is invalid in M16C/80 series.
Port output control is set by the function select registers A and B.
– –
Note: This does not apply when the free-run function is selected.