GMS81C2012/GMS81C2020
8-bit Timer Mode
HYUNDAI MicroElectronics
In the timer mode, the internal clock is used for counting
up. Thus, you can think of it as counting internal clock in-
put. The contents of TDRn are compared with the contents
of up-counter, Tn. If match is found, a timer 1 interrupt
(T1IF) is generated and the up-counter is cleared to 0.
Counting up is resumed after the up-counter is cleared.
As the value of TDRn is changeable by software, time in-
terval is set as you want
Start count
Source clock
2
3
n-2
n-1
n
1
4
2
3
0
1
0
Up-counter
n
TDR1
Match
Detect
Counter
Clear
T1IF interrupt
Figure 12-3 Timer Mode Timing Chart
Example: Make 2msꢁinterrupt using by Timer0 at 4MHz
LDM
LDM
TM0,#0FH
; divide by 32
TDR0,#125
; 8us x 125= 1ms
SET1 T0E
EI
; Enable Timer 0 Interrupt
; Enable Master Interrupt
When
TM0 = 0000 1111B (8-bit Timer mode, Prescaler divide ratio = 32)
TDR0 = 125D = 7DH
fXIN = 4 MHz
1
INTERRUPT PERIOD =
32 125 = 1 ms
×
×
4
106 Hz
×
TDR1
7D
MATCH
(TDR0 = T0)
Count Pulse
Period
7D
7C
7B
7A
8
s
µ
6
5
4
3
2
1
0
0
TIME
Interrupt period
= 8 s x 125
µ
Timer 1 (T1IF)
Interrupt
Occur interrupt
Occur interrupt
Occur interrupt
Figure 12-4 Timer Count Example
52
MAR. 2000 Ver 1.00
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