Mitsubishi microcomputers
M16C / 61 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Timer A
(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 1.16.2 lists timer specifications when counting a single-phase external signal.
Figure 1.16.7 shows the timer Ai mode register in event counter mode.
Table 1.16.3 lists timer specifications when counting a two-phase external signal. Figure 1.16.8 shows
the timer Ai mode register in event counter mode.
Table 1.16.2. Timer specifications in event counter mode (when not processing two-phase pulse 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 or software
• When the timer overflows or underflows, it reloads the reload register con
tents before continuing counting (Note)
1/ (FFFF16 - n + 1) for up count
Divide ratio
1/ (n + 1) for down count
Count start flag is set (= 1)
Count start flag is reset (= 0)
n : Set value
Count start condition
Count stop condition
Interrupt request generation timing The timer overflows or underflows
TAiIN pin function
TAiOUT pin function
Read from timer
Write to timer
Programmable I/O port or count source input
Programmable I/O port, pulse output, or up/down count select input
Count value can be read out by reading timer Ai register
• When counting stopped
When a value is written to timer Ai register, it is written to both reload register and counter
• When counting in progress
When a value is written to timer Ai register, it 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
Note: This does not apply when the free-run function is selected.
Timer Ai mode register
b7 b6 b5 b4 b3 b2 b1 b0
Symbol
TAiMR(i = 0, 1)
Address
039616, 039716
When reset
0016
0
0 1
Bit symbol
Bit name
Function
R W
R W
b1 b0
TMOD0
TMOD1
MR0
Operation mode select bit
0 1 : Event counter mode (Note 1)
0 : Pulse is not output
Pulse output function
select bit
(TAiOUT pin is a normal port pin)
1 : Pulse is output (Note 2)
(TAiOUT pin is a pulse output pin)
MR1
MR2
Count polarity
select bit (Note 3)
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 : TAiOUT pin's input signal (Note 4)
MR3
0 (Must always be fixed to “0” in event counter mode)
TCK0
Count operation type
select bit
0 : Reload type
1 : Free-run type
Invalid in event counter mode
Can be “0” or “1”
TCK1
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”.
Figure 1.16.7. Timer Ai mode register in event counter mode
75
MITSUBISHI [ Mitsubishi Group ]
