HT46R52A Holtek Semiconductor, HT46R52A Datasheet - Page 9

• Manufacturer Part Number: HT46R52A
• Description: (HT46R51A / HT46R52A) A/D Type 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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Interrupts
The device provides an external interrupt, an internal
timer/event counter interrupt, and an A/D converter in-
terrupt. The interrupt control register (INTC;0BH) con-
tains the interrupt control bits to set the enable/disable
and the interrupt request flags.
Once an interrupt subroutine is serviced, all the other in-
terrupts will be blocked (by clearing the EMI bit). This
scheme may prevent any further interrupt nesting. Other
interrupt requests may occur during this interval but only
the interrupt request flag is recorded. If a certain inter-
rupt requires servicing within the service routine, the
EMI bit and the corresponding bit of the INTC may be
set to allow interrupt nesting. If the stack is full, the inter-
rupt request will not be acknowledged, even if the re-
lated interrupt is enabled, until the SP is decremented. If
immediate service is desired, the stack must be pre-
vented from becoming full.
All these kinds of interrupts have a wake-up capability.
As an interrupt is serviced, a control transfer occurs by
pushing the program counter onto the stack, followed by
a branch to a subroutine at specified location in the pro-
gram memory. Only the program counter is pushed onto
the stack. If the contents of the register or status register
(STATUS) are altered by the interrupt service program
which corrupts the desired control sequence, the con-
tents should be saved in advance.
External interrupts are triggered by a high to low transi-
tion of INT and the related interrupt request flag (EIF; bit
4 of the INTC) will be set. When the interrupt is enabled,
the stack is not full and the external interrupt is active, a
subroutine call to location 04H will occur. The interrupt
request flag (EIF) and EMI bits will be cleared to disable
other interrupts.
Rev. 1.00
Bit No.
6~7
0
1
2
3
4
5
Label
PDF
OV
AC
TO
C
Z
C is set if an operation results in a carry during an addition operation or if a borrow does not
take place during a subtraction operation; otherwise C is cleared. C is also affected by a rotate
through carry instruction.
AC is set if an operation results in a carry out of the low nibbles in addition or no borrow from
the high nibble into the low nibble in subtraction; otherwise AC is cleared.
Z is set if the result of an arithmetic or logic operation is zero; otherwise Z is cleared.
OV is set if an operation results in a carry into the highest-order bit but not a carry out of the
highest-order bit, or vice versa; otherwise OV is cleared.
PDF is cleared by system power-up or executing the CLR WDT instruction. PDF is set by
executing the HALT instruction.
TO is cleared by system power-up or executing the CLR WDT or HALT instruction. TO is
set by a WDT time-out.
Unused bit, read as 0
Status (0AH) Register
9
The internal Timer/Event Counter interrupt is initialized
by setting the Timer/Event Counter interrupt request flag
(TF; bit 5 of the INTC), which is normally caused by a
timer overflow. After the interrupt is enabled, and the
stack is not full, and the TF bit is set, a subroutine call to
location 08H occurs. The related interrupt request flag
(TF) is reset, and the EMI bit is cleared to disable further
maskable interrupts.
The A/D converter interrupt is initialized by setting the
A/D converter request flag (ADF; bit 6 of the INTC),
caused by an end of A/D conversion. When the interrupt
is enabled, the stack is not full and the ADF is set, a sub-
routine call to location 0CH will occur. The related in-
terrupt request flag (ADF) will be reset and the EMI bit
cleared to disable further interrupts.
During the execution of an interrupt subroutine, other in-
terrupt acknowledgments 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.
External Interrupt
Timer/Event Counter Overflow
A/D Converter Interrupt
Function
Interrupt Source
HT46R51A/HT46R52A
Priority
August 24, 2006
1
2
3
Vector
0CH
04H
08H