Holtek HT49RA0 Manual page 10

It is recommended that a program not use the ²CALL
subroutine² within the interrupt subroutine. It¢s because
interrupts often occur in an unpredictable manner or re-
quire to be serviced immediately in some applications.
At this time, if only one stack is left, and enabling the in-
terrupt is not well controlled, operation of the ²call² in the
interrupt subroutine may damage the original control se-
quence.
LCD/RTC OSC Control Register
Two bit in (1FH) are for controlling LCD and RTC OSC.
Bit No. Label
0 RTCEN
1 LCDEN
¾
2~7
LCDEN and RTCEN may decide LCD and RTC On/Off condition on normal operation.
f Clock
S
Source
LCDEN, RTCEN=0, 0
f /4 LCD off, RTC off
SYS
WDT OSC LCD off, RTC off
RTC OSC
LCD off, RTC on
(WDT enable)
RTC OSC
LCD off, RTC off
(WDT disable)
Rev. 1.50
Oscillator Configuration
An external resistor between OSC1 and VSS in needed
and the resistance is about 12kW. The RC oscillator
provides a ±3% accuracy, the conditions are:
·
·
·
Controls RTC OSC enable (1=enabled; 0=disabled)
Controls LCD enable (1=enabled; 0=disabled)
Unused bit, read as ²0²
LCDC (1FH) Register
LCD/WDT Control Bits
LCDEN, RTCEN=0, 1
LCD off, RTC off
LCD off, RTC off
LCD off, RTC on
LCD off, RTC on
10
HT49RA0/HT49CA0
V =2.0V~3.6V
DD
Temp.= 0°C ~ 50°C
f =4MHz
SYS
O S C 1
R C O s c i l l a t o r
System Oscillator
Function
LCDEN, RTCEN=1, 0
LCD on, RTC off
LCD on, RTC off
LCD on, RTC on
LCD on, RTC on
LCDEN, RTCEN=1, 1
LCD on, RTC off
LCD on, RTC off
LCD on, RTC on
LCD on, RTC on
March 20, 2014