Timer A
M30240 Group
Rev. H Sep 18, 2003 Page 70 of 139
1.2.21.2 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 1.19 lists the timer specifications when counting a single-phase external
signal. Figure 1.64 shows Timer Ai mode register in event counter mode, Note: Timer Ai register’s val-
ue can be indeterminate when the count starts.
Table 1.19: Timer specification in event counter mode (when not processing two-phase pulse signal)
Note: Timer Ai register ’s value can be indeterminate when the count starts.
Figure 1.64: Timer Ai mode register in event counter mode, single signal
Item Specification
Count source • External signals input to TAiIN pin (effective edge can be selected by software)
• TB2 overflow, TAj overflow
Count operation • Up count or down count can be selected by external signal of software
• When the timer overflows or underflows, it loads the reload register contents before continuing counting
(However, this does not apply when the free-run function is selected)
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 When the timer underflows 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
Read from timer Count value can be read out by reading Timer Ai register
Write to timer
• When counting is stopped and a value is written to Timer Ai register , it is written to both reload register and
counter
• When counting is in progress and a value is written to Timer Ai register, it is written only to reload register
(to be transferred to counter at the next reload time)
Select function
• Free-run count function (Note)
When the timer overflows or underflows, the reload register’s content is not reloaded.
• Pulse output function
Each time the timer underflows, the TAiOUT pin’s polarity is reversed
Note 1: In event counter mode, the count source is selected by the event / trigger select bit
(addresses 038216 and 038316).
Note 2: The settings of the corresponding port register and port direction register are invalid.
Note 3: Valid only when counting an external signal.
Note 4: When an “L” signal is input to the TAiOUT
pin, the downcount is activated. When “H”,
the upcount is activated. Set the corresponding port direction register to “0”.
Note 5: This value can be indeterminate when the count starts.
Timer Ai mode register
Symbol Address When reset
TAiMR(i = 0, 1) 039616, 039716 0016
WR
b7 b6 b5 b4 b3 b2 b1 b0
Operation mode select bit
0 1 : Event counter mode (Note 1)
b1 b0
TMOD0
MR0 Pulse output function
select bit
0 : Pulse is not output
(TA iOUT pin is a normal port pin)
1 : Pulse is output (Note 2)
(TA iOUT pin is a pulse output pin)
Count polarity
select bit (Note 3)
MR2
MR1
MR3 0 (Must always be fixed to “0” in event counter mode)
TCK0 Count operation type
select bit
01
0
0 : Counts external signal's falling edge
1 : Counts external signal's rising edge
Up/down switching
cause select bit
0 : Up/down flag's content
1 : TA iOUT pin's input signal (Note 4)
0 : Reload type
1 : Free-run type (Note 5)
Bit symbol Bit name Function RW
TCK1 Invalid in event counter mode
Can be “0” or “1”
TMOD1
Note 1: In event counter mode, the count source is selected by the event / trigger select bit
(addresses 038216 and 038316).
Note 2: The settings of the corresponding port register and port direction register are invalid.
Note 3: Valid only when counting an external signal.
Note 4: When an “L” signal is input to the TAiOUT
pin, the downcount is activated. When “H”,
the upcount is activated. Set the corresponding port direction register to “0”.
Note 5: This value can be indeterminate when the count starts.
Timer Ai mode register
Symbol Address When reset
TAiMR(i = 0, 1) 039616, 039716 0016
WR
b7 b6 b5 b4 b3 b2 b1 b0
Operation mode select bit
0 1 : Event counter mode (Note 1)
b1 b0
TMOD0
MR0 Pulse output function
select bit
0 : Pulse is not output
(TA iOUT pin is a normal port pin)
1 : Pulse is output (Note 2)
(TA iOUT pin is a pulse output pin)
Count polarity
select bit (Note 3)
MR2
MR1
MR3 0 (Must always be fixed to “0” in event counter mode)
TCK0 Count operation type
select bit
01
0
0 : Counts external signal's falling edge
1 : Counts external signal's rising edge
Up/down switching
cause select bit
0 : Up/down flag's content
1 : TA iOUT pin's input signal (Note 4)
0 : Reload type
1 : Free-run type (Note 5)
Bit symbol Bit name Function RW
TCK1 Invalid in event counter mode
Can be “0” or “1”
TMOD1