HT82A520R HOLTEK [Holtek Semiconductor Inc], HT82A520R Datasheet - Page 21

• Manufacturer Part Number: HT82A520R
• Description: Full Speed USB 8-Bit OTP MCU with SPI
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

When the Timer/Event Counter is read or if data is written
to the preload registers, the clock is inhibited to avoid er-
rors, however as this may result in a counting error, this
should be taken into account by the programmer. Care
must be taken to ensure that the timers are properly in-
itialised before using them for the first time. The associ-
ated timer interrupt enable bits in the interrupt control
register must be properly set otherwise the internal inter-
rupt associated with the timer will remain inactive. The
edge select, timer mode and clock source control bits in
timer control register must also be correctly set to ensure
the timer is properly configured for the required applica-
tion. It is also important to ensure that an initial value is
first loaded into the timer register before the timer is
switched on; this is because after power-on the initial
value of the timer register is unknown. After the timer has
been initialised the timer can be turned on and off by con-
trolling the enable bit in the timer control register. Note
that setting the timer enable bit high to turn the timer on,
should only be executed after the timer mode bits have
been properly setup. Setting the timer enable bit high to-
gether with a mode bit modification, may lead to improper
timer operation if executed as a single timer control regis-
ter byte write instruction.
When the Timer/Event counter overflows, its corre-
sponding interrupt request flag in the interrupt control
org 04h
reti
org 08h
reti
org 0ch
jmp tmr0int
org 010h
reti
:
org 20h
:
;internal Timer/Event Counter interrupt routine
tmrint:
:
; Timer/Event Counter main program placed here
:
reti
:
begin:
;setup Timer/Event Counter registers
mov a,0e8h
mov tmrl,a
mov a,09bh
mov tmrh,a
mov a,080h
mov tmrc,a
mov a,009h
mov intc0,a
:
set tmrc.4
Rev.1.00
; USB interrupt vector
; external interrupt vector
; Timer/Event Counter interrupt vector
; jump here when Timer/Event Counter overflows
; SPI interrupt vector
; main program
; setup low byte preload value for Timer/Event Counter
; low byte must be setup before high byte
; setup high byte preload value for Timer/Event Counter
;
; setup Timer control register TMRC
; Timer/Event Counter clock source is fSYS/4
; setup interrupt register
; enable master interrupt and timer interrupts
; start Timer/Event Counter _ note mode bits must be previously setup
21
register will be set. If the timer interrupt is enabled this
will in turn generate an interrupt signal. However irre-
spective of whether the timer interrupt is enabled or not,
a Timer/Event counter overflow will also generate a
wake-up signal if the device is in a Power-down condi-
tion. This situation may occur if the Timer/Event Counter
is in the Event Counting Mode and if the external signal
continues to change state. In such a case, the
Timer/Event Counter will continue to count these exter-
nal events and if an overflow occurs the device will be
woken up from its Power-down condition. To prevent
such a wake-up from occurring, the timer interrupt re-
quest flag should first be set high before issuing the
HALT instruction to enter the Power Down Mode.
Timer Program Example
This program example shows how the Timer/Event
Counter registers are setup, along with how the inter-
rupts are enabled and managed. Note how the
Timer/Event Counter is turned on, by setting bit 4 of the
Timer Control Register. The Timer/Event Counter can
be turned off in a similar way by clearing the same bit.
This example program sets the Timer/Event Counter
tobe in the timer mode, which uses the internal system
clock as the clock source.
HT82A520R/HT82A620R
October 23, 2009