HT46R47-H
transient occurs again. In other words, only one cycle
measurement can be done. Until setting the TON, the
cycle measurement will function again as long as it re-
ceives further transient pulse. Note that, in this operat-
ing mode, the timer/event counter starts counting not
according to the logic level but according to the transient
edges. In the case of counter overflows, the counter is
reloaded from the timer/event counter preload register
and issues the interrupt request just like the other two
modes. To enable the counting operation, the timer ON
bit (TON; bit 4 of TMRC) should be set to 1. In the pulse
width measurement mode, the TON will be cleared au-
tomatically after the measurement cycle is completed.
But in the other two modes the TON can only be reset by
instructions. The overflow of the timer/event counter is
one of the wake-up sources. No matter what the opera-
tion mode is, writing a 0 to ETI can disable the interrupt
service.
In the case of timer/event counter OFF condition, writing
data to the timer/event counter preload register will also
reload that data to the timer/event counter. But if the
timer/event counter is turned on, data written to it will
only be kept in the timer/event counter preload register.
The timer/event counter will still operate until overflow
occurs. When the timer/event counter (reading TMR) is
read, the clock will be blocked to avoid errors. As clock
blocking may results in a counting error, this must be
taken into consideration by the programmer.
The bit0~bit2 of the TMRC can be used to define the
pre-scaling stages of the internal clock sources of
timer/event counter. The definitions are as shown. The
overflow signal of timer/event counter can be used to
generate the PFD signal.
Bit No.
Label
Function
Defines the prescaler stages, PSC2, PSC1, PSC0=
000: fINT=fSYS
001: fINT=fSYS/2
010: fINT=fSYS/4
011: fINT=fSYS/8
100: fINT=fSYS/16
101: fINT=fSYS/32
110: fINT=fSYS/64
111: fINT=fSYS/128
0
1
2
PSC0
PSC1
PSC2
Defines the TMR active edge of the timer/event counter:
In Event Counter Mode (TM1,TM0)=(0,1):
1:count on falling edge;
3
TE
0:count on rising edge
In Pulse Width measurement mode (TM1,TM0)=(1,1):
1: start counting on the rising edge, stop on the falling edge;
0: start counting on the falling edge, stop on the rising edge
4
5
TON
Enable or disable the timer counting (0=disable; 1=enable)
¾
Unused bits, read as ²0²
Defines the operating mode (TM1, TM0)=
01=Event count mode (external clock)
10=Timer mode (internal clock)
11=Pulse width measurement mode
00=Unused
6
7
TM0
TM1
TMRC (0EH) Register
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Timer/Event Counter
Rev. 1.30
15
March 1, 2006
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
