HT82K74EE HOLTEK [Holtek Semiconductor Inc], HT82K74EE Datasheet - Page 21

• Manufacturer Part Number: HT82K74EE
• Description: 27MHz Keyboard/ Mouse TX 8-Bit MCU
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

must also be noted that to read the contents of the low
byte register, a read to the high byte register must first
be executed to latch the contents of the low byte buffer
from its associated low byte register. After this has been
done, the low byte register can be read in the normal
way. Note that reading the low byte timer register di-
rectly will only result in reading the previously latched
contents of the low byte buffer and not the actual con-
tents of the low byte timer register.
Timer Control Register - TMRC
The flexible features of the Holtek microcontroller
Timer/Event Counters enable them to operate in three
different modes, the options of which are determined by
the contents of the Timer Control Register TMRC. To-
gether with the TMRL and TMRH registers, these three
registers control the full operation of the Timer/Event
Counter. Before the timer can be used, it is essential that
the TMRC register is fully programmed with the right
data to ensure its correct operation, a process that is
normally carried out during program initialisation.
To choose which of the three modes the timer is to oper-
ate in, the timer mode, the event counting mode or the
pulse width measurement mode, bits TM0 and TM1
must be set to the required logic levels. The timer-on bit
TON or bit 4 of the TMRC register provides the basic
Rev. 1.00
Timer/Event Counter Control Register
Timer Mode Timing Chart
21
on/off control of the timer, setting the bit high allows the
counter to run, clearing the bit stops the counter. If the
timer is in the event count or pulse width measurement
mode the active transition edge level type is selected by
the logic level of the TE or bit 3 of the TMRC register.
Configuring the Timer Mode
In this mode, the timer can be utilised to measure fixed
time intervals, providing an internal interrupt signal each
time the counter overflows. To operate in this mode, bits
TM1 and TM0 of the TMRC register must be set to 1 and
0 respectively. In this mode, the internal clock is used as
the timer clock. The timer-on bit, TON, must be set high
to enable the timer to run. Each time an internal clock
high to low transition occurs, the timer increments by
one. When the timer is full and overflows, the timer will
be reset to the value already loaded into the preload reg-
ister and continue counting. If the timer interrupt is en-
abled, an interrupt signal will also be generated. The
timer interrupt can be disabled by ensuring that the ETI
bit in the INTC register is cleared to zero.
Note: The timer overflow can t wake-up the MCU from
Power Down Mode.
HT82K74E/HT82K74EE
December 15, 2009