HT48CA3 Holtek Semiconductor Inc, HT48CA3 Datasheet - Page 8

• Manufacturer Part Number: HT48CA3
• Description: 8-Bit Remote Type MCU
• Manufacturer: Holtek Semiconductor Inc

During the execution of an interrupt subroutine, other in-
terrupt acknowledge signals are held until the RETI in-
struction is executed or the EMI bit and the related
interrupt control bit are set to 1 (if the stack is not full). To
return from the interrupt subroutine, RET or RETI
may be invoked. RETI will set the EMI bit to enable an in-
terrupt service, but RET will not.
Interrupts, occurring in the interval between the rising
edges of two consecutive T2 pulses, will be serviced on
the latter of the two T2 pulses, if the corresponding inter-
rupts are enabled. In the case of simultaneous requests
the following table shows the priority that is applied.
These can be masked by resetting the EMI bit.
The Timer/Event Counter 0/1 interrupt request flag
(T0F/T1F), external interrupt request flag (EIF), enable
Timer/Event Counter 0/1 interrupt bit (ET0I/ET1I), en-
able external interrupt bit (EEI) and enable master inter-
rupt bit (EMI) constitute an interrupt control register
(INTC) which is located at 0BH in the data memory. EMI,
EEI, ET0I and ET1I are used to control the enabling/dis-
abling of interrupts. These bits prevent the requested in-
terrupt from being serviced. Once the interrupt request
flags (T0F, T1F, EIF) are set, they will remain in the INTC
register until the interrupts are serviced or cleared by a
software instruction.
It is recommended that a program does not use the
terrupts often occur in an unpredictable manner or
need to be serviced immediately in some applications.
If only one stack is left and enabling the interrupt is not
well controlled, the original control sequence will be dam-
aged once the CALL operates in the interrupt subrou-
tine.
Rev. 1.40
External Interrupt
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
CALL subroutine within the interrupt subroutine. In-
Register
(0BH)
INTC
Interrupt Source
Bit No.
0
1
2
3
4
5
6
7
Label
ET0I
ET1I
EMI
T0F
T1F
EEI
EIF
Priority
1
2
3
Controls the master (global) interrupt (1=enabled; 0=disabled)
Controls the external interrupt (1=enabled; 0=disabled)
Controls the Timer/Event Counter 0 interrupt (1=enabled; 0=disabled)
Controls the Timer/Event Counter 1 interrupt (1=enabled; 0=disabled)
External interrupt request flag (1= active; 0= inactive)
Internal Timer/Event Counter 0 request flag (1=active; 0=inactive)
Internal Timer/Event Counter 1 request flag (1=active; 0=inactive)
Unused bit, read as 0
Vector
0CH
04H
08H
INTC register
8
Oscillator Configuration
There are 2 oscillator circuits in the MCU.
There are 2 oscillator circuits implemented in the mi-
cro-controller.
Both of them are designed for system clocks, namely
the RC oscillator and the crystal oscillator, which are de-
termined by options. No matter what oscillator type is
selected, the signal provides the system clock. The
HALT mode stops the system oscillator and resists the
external signal to conserve power.
If an RC oscillator is used, an external resistor between
OSC1 and VSS is required and the resistance should
range from 100k to 820k . The system clock, divided
by 4, is available on OSC2, which can be used to syn-
chronize external logic. The internal RC oscillator pro-
vides the most cost effective solution. However, the
frequency of oscillation may vary with VDD, tempera-
tures and the chip itself due to process variations. It is,
therefore, not suitable for timing sensitive operations
where an accurate oscillator frequency is desired.
If the crystal oscillator is used, a crystal across OSC1
and OSC2 is needed to provide the feedback and phase
shift required for the oscillator, and no other external
components are demanded. Instead of a crystal, the
resonator can also be connected between OSC1 and
OSC2 to get a frequency reference, but two external ca-
pacitors in OSC1 and OSC2 are required.
The WDT oscillator is a free running on-chip RC oscilla-
tor, and no external components are required. Even if
the system enters the power down mode, the system
clock is stopped, but the WDT oscillator still works with a
Function
System oscillator
HT48CA3
July 16, 2003