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12. Timer
page 92
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Item
Specification
Count source
f1, f2, f8, f32, fC32
Count operation
Down-count
When the timer underflows, it reloads the reload register contents and continues counting
Divide ratio
1/(n+1)
n: set value of TAi register (i= 0 to 4)
000016 to FFFF16
Count start condition
Set TAiS bit in the TABSR register to “1” (= start counting)
Count stop condition
Set TAiS bit to “0” (= stop counting)
Interrupt request generation timing
Timer underflow
TAiIN pin function
I/O port or gate input
TAiOUT pin function
I/O port or pulse output
Read from timer
Count value can be read by reading TAi register
Write to timer
When not counting and until the 1st count source is input after counting start
Value written to TAi register is written to both reload register and counter
When counting (after 1st count source input)
Value written to TAi register is written to only reload register
(Transferred to counter when reloaded next)
Select function
Gate function
Counting can be started and stopped by an input signal to TAiIN pin
Pulse output function
Whenever the timer underflows, the output polarity of TAiOUT pin is inverted.
When not counting, the pin outputs a low.
12.1.1. Timer Mode
In timer mode, the timer counts a count source generated internally (see Table 12.1.1.1). Figure 1.2.1.1.1
shows TAiMR register in timer mode.
Table 12.1.1.1. Specifications in Timer Mode
Note 1: The port direction bit for the TAiIN pin must be set to “0” (= input mode).
Timer Ai mode register (i=0 to 4)
Symbol
Address
After reset
TA0MR to TA4MR
039616 to 039A16
0016
Bit name
Function
Bit symbol
RW
b7
b6
b5
b4
b3
b2
b1
b0
Operation mode
select bit
0 0 : Timer mode
b1 b0
TMOD1
TMOD0
MR0
Pulse output function
select bit
0 : Pulse is not output
(TAiOUT pin is a normal port pin)
1 : Pulse is output
(TAiOUT pin is a pulse output pin)
Gate function select bit
0 0 :
Gate function not available
0 1 :
(TAiIN pin functions as I/O port)
1 0 : Counts while input on the TAiIN pin
is low
(Note 1)
1 1 : Counts while input on the TAiIN pin
is high
(Note 1)
b4 b3
MR2
MR1
MR3
Must be set to “0” in timer mode
0 0 : f1 or f2
0 1 : f8
1 0 : f32
1 1 : fC32
b7 b6
TCK1
TCK0
Count source select bit
00
0
RW
}
Figure 12.1.1.1. Timer Ai Mode Register in Timer Mode