HT48R50A-1/HT48C50-1
Bit No.
Label
EMI
EEI
Function
0
1
2
3
4
5
6
7
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)
ET0I
ET1I
EIF
T0F
T1F
¾
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 ²0²
INTC (0BH) Register
During the execution of an interrupt subroutine, other in-
terrupt acknowledge signals are held until the ²RETI² 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, ²RET² or ²RETI²
may be invoked. RETI will set the EMI bit to enable an in-
terrupt service, but RET will not.
Oscillator configuration
There are 3 oscillator circuits in the microcontroller.
V
D
D
O
S
C
1
O
S
C
1
4
7
0
p
F
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.
S
Y
S
O
S
C
2
O
S
C
2
N
M
O
S
O
p
e
n
D
r
a
i
n
C
r
y
s
t
a
l
O
s
c
i
l
l
a
t
o
r
R
C
O
s
c
i
l
l
a
t
o
r
(
I
n
c
l
u
d
e
3
2
7
6
8
H
z
)
System Oscillator
All of them are designed for system clocks, namely the
external RC oscillator, the external Crystal oscillator and
the internal RC oscillator, which are determined by op-
tions. No matter what oscillator type is selected, the sig-
nal provides the system clock. The HALT mode stops
the system oscillator and ignores an external signal to
conserve power.
No.
a
Interrupt Source
External Interrupt
Priority Vector
1
2
3
04H
08H
0CH
b
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
c
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 or
disabling of interrupts. These bits prevent the requested
interrupt 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.
If an RC oscillator is used, an external resistor between
OSC1 and VDD is required and the resistance must
range from 24kW to 1MW. The system clock, divided by
4, is available on OSC2, which can be used to synchro-
nize external logic. The RC oscillator provides the most
cost effective solution. However, the frequency of oscil-
lation may vary with VDD, temperatures and the chip it-
self due to process variations. It is, therefore, not
suitable for timing sensitive operations where an accu-
rate 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. No other external compo-
nents are required. In stead of a crystal, a resonator can
also be connected between OSC1 and OSC2 to get a
frequency reference, but two external capacitors in
OSC1 and OSC2 are required. If the internal RC oscilla-
tor is used, the OSC1 and OSC2 can be selected as
general I/O lines or an 32768Hz crystal oscillator (RTC
It is recommended that a program does not use the
²CALL subroutine² within the interrupt subroutine. In-
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 ²CALL² operates in the interrupt subrou-
tine.
Rev. 2.00
10
March 8, 2006
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
