HT45F43 datasheet(63/152 Pages) HOLTEK

63 / 152 page

For the 16-bit Timer/Event Counter which has both low byte and high byte timer registers, accessing

these registers is carried out in a specific way. It must be noted when using instructions to preload data

into the low byte timer register, namely TMR1L, the data will only be placed in a low byte buffer and

not directly into the low byte timer register. The actual transfer of the data into the low byte timer

executed. On the other hand, using instructions to preload data into the high byte timer register will

result in the data being directly written to the high byte timer register. At the same time the data in the

low byte buffer will be transferred into its associated low byte timer register. For this reason, the low

byte timer register should be written first when preloading data into the 16-bit timer registers. It must

also be noted that to read the contents of the low byte timer register, a read to the high byte timer

byte buffer. After this has been done, the low byte timer register can be read in the normal way. Note

that reading the low byte timer register will result in reading the previously latched contents of the low

byte buffer and not the actual contents of the low byte timer register.

Timer Control Registers

- TMR0C, TMR1C

The flexible features of the Holtek microcontroller Timer/Event Counters enable them to operate in

four different modes, the options of which are determined by the contents of their respective control

It is the Timer Control Register together with its corresponding timer registers that control the full

operation of the Timer/Event Counters. Before the timers can be used, it is essential that the

appropriate Timer Control 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 four modes the timer is to operate in, either in the timer mode, the external

event counting mode, the internal event counter mode, or the pulse width measurement mode, bits 7

and 6 of the Timer Control Register, which are known as the bit pair T0M1/T0M0 or T1M1/T1M0

respectively, depending upon which timer is used, must be set to the required logic levels. The

timer-on bit, which is bit 4 of the Timer Control Register and known as T0ON or T1ON, depending

upon which timer is used, provides the basic on/off control of the respective timer. Setting the bit high

allows the counter to run, clearing the bit stops the counter. For timers that have prescalers, bits 0~2 of

the Timer Control Register determine the division ratio of the input clock prescaler. The prescaler bit

settings have no effect if an external clock source is used. 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 bit 3 of

the Timer Control Register which is known as T0E or T1E depending upon which timer is used. An

additional T1S bit in the TMR1C register is used to determine the clock source for Timer/Event

Counter 1.

Configuring the Timer Mode

In this mode, the Timer/Event Counter can be utilised to measure fixed time intervals, providing an

internal interrupt signal each time the Timer/Event Counter overflows. To operate in this mode, the

Operating Mode Select bit pair, T0M1/T0M0 or T1M1/T1M0, in the Timer Control Register must be

set to the correct value as shown.

Control Register Operating Mode

Select Bits for the Timer Mode

Bit7

Bit6

In this mode the internal clock, fSYS , is used as the internal clock for 8-bit Timer/Event Counter 0 and

fSUB or fSYS/4 is used as the internal clock for 16-bit Timer/Event Counter 1. However, the clock source,

fSYS, for 8-bit timer is further divided by a prescaler, the value of which is determined by the Prescaler

Rate Select bits T0PSC2~T0PSC0, which are bits 2~0 in the Timer Control Register. After the other

bits in the Timer Control Register have been setup, the enable bit T0ON or T1ON, which is bit 4 of the

Timer Control Register, can be set high to enable the Timer/Event Counter to run. Each time an

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

Rev. 1.20

September 15, 2011

HT45F43 датащи(PDF) 63 Page - Holtek Semiconductor Inc

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