ht82k68a Holtek Semiconductor Inc., ht82k68a Datasheet - Page 9

• Manufacturer Part Number: ht82k68a
• Description: Ht82k68a -- Multimedia Keyboard Encoder 8-bit Mask Mcu
• Manufacturer: Holtek Semiconductor Inc.

Interrupt
The HT82K68A provides an internal timer counter inter-
rupt and an external interrupt shared with PC2. The in-
terrupt control register (INTC;0BH) contains the
interrupt control bits to set not only the enable/disable
status but also the interrupt request flags.
Once an interrupt subroutine is serviced, all other inter-
rupts 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 interrupt have the 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 the specified location in the
program memory. Only the program counter is pushed
Rev. 1.70
Bit No.
Bit No.
3, 6~7
6, 7
0
1
2
3
4
5
0
1
2
4
5
Label
Label
ET0I
PDF
EMI
T0F
EEI
OV
EIF
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 if 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 logical 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 when either a system power-up or executing the CLR WDT instruction.
PDF is set by executing a HALT instruction.
TO is cleared by a system power-up or executing the CLR WDT or HALT instruction.
TO is set by a WDT time-out.
Unused bit, read as 0
Controls the master (global) interrupt (1= enabled; 0= disabled)
Control the external interrupt
Controls the timer counter interrupt (1= enabled; 0= disabled)
Unused bit, read as 0
External interrupt flag
Internal timer counter request flag (1= active; 0= inactive)
Status (0AH) Register
INTC (0BH) Register
9
onto the stack. If the contents of the register and Status
register (STATUS) are altered by the interrupt service
program which corrupt the desired control sequence,
the contents should be saved in advance.
The internal timer counter interrupt is initialized by set-
ting the timer counter interrupt request flag (T0F; bit 5 of
INTC), which is normally caused by a timer counter
overflow. When the interrupt is enabled, and the stack is
not full and the T0F bit is set, a subroutine call to location
08H will occur. The related interrupt request flag (T0F)
will be reset and the EMI bit cleared to disable further in-
terrupts.
The external interrupt is shared with PC2. The external
interrupt is activated, the related interrupt request flag
(EIF; bit4 of INTC) is then set. When the interrupt is en-
abled, 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 also be
cleared to disable other interrupts.
The external interrupt (PC2) can be triggered by a high
to low transition, or a low to high transition of the PC2,
which is dependent on the output level of the PE0. When
PE0 is output high, the external interrupt is triggered by
Function
Function
December 26, 2005
HT82K68A