HT49R50 datasheet(16/59 Pages) HOLTEK

16 / 59 page

HT49R50

October 22, 1999

able/disable status of interrupts. These bits

prevent the requested interrupt from being ser-

viced. Once the interrupt request flags (RTF,

TBF, T0F, T1F, EIF1, EIF0) are all set, they re-

main in the INTC1 or INTC0 respectively until

the interrupts are serviced or cleared by a soft-

ware instruction.

It is recommended that a program not use the "CALL

subroutine" within the interrupt subroutine. It s

because interrupts often occur in an unpredictable

manner or require to be serviced immediately in

some applications. At this time, if only one stack is

left, and enabling the interrupt is not well con-

trolled, operation of the "call" in the interrupt

subroutine may damage the original control se-

quence.

Oscillator configuration

The HT49R50 provides two oscillator circuits

for system clocks, i.e., RC oscillator and crystal

oscillator, determined by options. No matter

what type of oscillator is selected, the signal is

used for the system clock. The HALT mode

stops the system oscillator and ignores external

signal to conserve power.

Of the two oscillators, if the RC oscillator is

used, an external resistor between OSC1 and

VSS is required, and the range of the resistance

should be from 100kW to 1MW. The system

clock, divided by 4, is available on OSC2 with

pull-high resistor, which can be used to syn-

chronize external logic. The RC oscillator pro-

vides the most cost effective solution. However,

the frequency of the oscillation may vary with

VDD, temperature, and the chip itself due to

process variations. It is therefore, not suitable

for timing sensitive operations where accurate

oscillator frequency is desired.

On the other hand, if the crystal oscillator is se-

lected, a crystal across OSC1 and OSC2 is

needed to provide the feedback and phase shift

required for the oscillator, and no other exter-

nal components are required. A resonator may

be connected between OSC1 and OSC2 to re-

place the crystal and to get a frequency refer-

ence, but two external capacitors in OSC1 and

OSC2 are required.

There is another oscillator circuit designed for

the real time clock. In this case, only the

32.768kHz crystal oscillator can be applied.

The crystal should be connected between OSC3

and OSC4.

The RTC oscillator circuit can be controlled to

oscillate quickly by setting the "QOSC" bit (bit

4 of RTCC). It is recommended to turn on the

quick oscillating function upon power on, and

turn it off after 2 seconds.

The WDT oscillator is a free running on-chip

RC oscillator, and no external components are

required. Although the system enters the

power down mode, the system clock stops, and

the WDT oscillator still works with a period of

approximately 78ms. The WDT oscillator can be

disabled by options to conserve power.

OS C 3

OS C 4

RTC oscillator

C r y s t a l O s c illa t o r

R C O s c illa t o r

OS C 1

OS C 2

OS C 1

OS C 2

f SYS /4

V DD

System oscillator

HT49R50 Folha de dados(PDF) 16 Page - Holtek Semiconductor Inc

HT49R50 Folha de dados(HTML) 16 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

Folha de dados Download

Ligação URL