HT36M4
Writing TMR0L only writes the data into a low byte
buffer, and writing TMR0H will write the data and the
contents of the low byte buffer into the Timer/Event
Counter 0 preload register (16-bit) simultaneously. The
Timer/Event Counter 0 Preload register is changed by
writing TMR0H operations and writing TMR0L will keep
the Timer/Event Counter 0 Preload register unchanged.
TO
0
RESET Conditions
RES reset during power-up
RES reset during normal operation
RES wake-up HALT
0
u
1
u
1
u
0
1
WDT time-out during normal operation
WDT wake-up HALT
1
Reading TMR0H will also latch the TMR0L into the low
byte buffer to avoid a false timing problem. Reading
TMR0L returns the contents of the low byte buffer. In
other words, the low byte of the Timer/Event Counter 0
cannot be read directly. It must read the TMR0H first to
make the low byte contents of the Timer/Event Counter
0 latched into the buffer.
Note: ²u² stands for ²unchanged²
To guarantee that the system oscillator has started and
stabilized, the SST (System Start-up Timer) provides an
extra-delay of 1024 system clock pulses during system
power up or when the system awakes from a HALT
state.
There are three registers related to the Timer/Event
Counter 1; TMR1H (0FH), TMR1L (10H), TMR1C (11H).
The Timer/Event Counter 1 operates in the same man-
ner as Timer/Event Counter 0.
When a system power-up occurs, the SST delay is
added during the reset period. But when the reset co-
mes from the RES pin, the SST delay is disabled. Any
wake-up from HALT will enable the SST delay.
The TMR0C is the Timer/Event Counter 0 control regis-
ter, which defines the Timer/Event Counter 0 options.
The Timer/Event Counter 1 has the same options with
Timer/Event Counter 0 and is defined by TMR1C.
The functional units chip reset status are shown below.
Program Counter
Interrupt
000H
Disable
Clear
The Timer/Event Counter control registers define the
operating mode, counting enable or disable and active
edge.
Prescaler
Clear. After master reset,
WDT begins counting
WDT
The TM0, TM1 bits define the operating mode. The
Event count mode is used to count external events,
which means the clock source comes from an external
(TMR) pin. The Timer mode functions as a normal timer
with the clock source coming from the instruction clock.
The pulse width measurement mode can be used to
count the high or low level duration of the external signal
(TMR). The counting is based on the instruction clock.
Timer/Event Counter (0/1) Off
Input/output ports
Stack Pointer
Input mode
Points to the top of the
stack
Timer/Event Counter
Two timer/event counters are implemented in the
HT36M4. The Timer/Event Counter 0 and Timer/Event
Counter 1 contain 16-bit programmable count-up coun-
ters and the clock comes from the system clock divided
by 4.
In the Event count or Timer mode, once the timer/event
counter starts counting, it will count from the current
contents in the timer/event counter to FFFFH. Once
overflow occurs, the counter is reloaded from the
Timer/Event Counter Preload register and simulta-
neously generates the corresponding interrupt request
flag (T0F/T1F; bit 5/6 of INTC).
There are three registers related to Timer/Event Coun-
ter 0; TMR0H (0CH), TMR0L (0DH), TMR0C (0EH).
Bit No.
Label
Function
0~2
¾
Unused bit, read as ²0²
Defines the TMR active edge of the Timer/Event Counter 0
(0=active on low to high; 1=active on high to low)
3
TE
4
5
TON
Enable/disable timer counting (0=disable; 1=enable)
¾
Unused bit, read as ²0²
Defines the operating mode
01=Event count mode (External clock)
10=Timer mode (Internal clock)
11=Pulse width measurement mode
00=Unused
6
7
TM0
TM1
TMR0C/TMR1C (0EH/11H) Register
Rev. 1.10
13
March 14, 2007
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
