GD32F20x User Manual
431
Down counting mode
In this mode, the counter counts down continuously from the counter-reload value, which is
defined in the TIMERx_CAR register, to 0 in a count-down direction. Once the counter
reaches to 0, the counter restarts to count again from the counter-reload value. If the repetition
counter is set, the update event will be generated after (TIME1) times of underflow.
Otherwise the update event is generated each time when underflows. The counting direction
bit DIR in the TIMERx_CTL0 register should be set to 1 for the down-counting mode.
When the update event is set by the UPG bit in the TIMERx_SWEVG register, the counter
value will be initialized to the counter-reload value and generates an update event.
If set the UPDIS bit in TIMERx_CTL0 register, the update event is disabled.
When an update event occurs, all the registers (repetition counter, auto reload register,
prescaler register) are updated.
The following figures show some examples of the counter behavior in different clock
frequencies when TIMERx_CAR=0x63.
Figure 18-55. Down-counter timechart, PSC=0/1
CEN
CNT_CLK(PSC_CLK)
CNT_REG
05
04
03
02
01
00
63
62
61
60
5F
5E
5C
5B
Update event (UPE)
Update interrupt flag (UPIF)
CNT_REG
04
03
Update event (UPE)
Update interrupt flag (UPIF)
Hardware set
Software clear
Hardware set
PSC = 0
PSC = 1
TIMER_CK
5A
00
01
02
63
62
61
CNT_CLK(PSC_CLK)
Summary of Contents for GD32F20 Series
Page 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Page 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Page 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Page 385: ...GD32F20x User Manual 385 ...
Page 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...