HT46R14
time-out or executing the
²CLR
WDT² or
²HALT²
in-
struction. The PDF flag can be affected only by exe-
cuting the
²HALT²
or
²CLR
WDT² instruction or a
system power-up.
The Z, OV, AC and C flags generally reflect the status of
the latest operations.
In addition, on entering the interrupt sequence or exe-
cuting the subroutine call, the status register will not be
pushed onto the stack automatically. If the contents of
the status are important and if the subroutine can cor-
rupt the status register, precautions must be taken to
save it properly.
Interrupt
The devices provides two external interrupts, two inter-
nal timer/event counter 0/1 interrupts, one comparator
interrupt, and A/D converter interrupt. The interrupt con-
trol register 0 (INTC0;0BH) and interrupt control register
1 (INTC1;1EH) both contain the interrupt control bits
that are used to set the enable/disable status and inter-
rupt request flags.
Once an interrupt subroutine is serviced, other inter-
rupts are all blocked (by clearing the EMI bit). This
scheme may prevent any further interrupt nesting. Other
interrupt requests may take place during this interval,
but only the interrupt request flag will be recorded. If a
certain interrupt requires servicing within the service
routine, the EMI bit and the corresponding bit of the
INTC0 or of INTC1 may be set in order to allow interrupt
nesting. Once the stack is full, the interrupt request will
not be acknowledged, even if the related interrupt is en-
abled, until the SP is decremented. If immediate service
is desired, the stack should be prevented from becom-
ing full.
All these interrupts can support a wake-up function. As
an interrupt is serviced, a control transfer occurs by
pushing the contents of the program counter onto the
Bit No.
0
Label
C
stack followed by a branch to a subroutine at the speci-
fied location in the ROM. Only the contents of the pro-
gram counter is pushed onto the stack. If the contents of
the register or of the status register (STATUS) is altered
by the interrupt service program which corrupts the de-
sired control sequence, the contents should be saved in
advance.
External interrupts are triggered by a high to low transi-
tion of INT0 or INT1, and the related interrupt request
flag (EI0F;bit 4 of the INTC0, EI1F;bit 5 of the INTC0) is
set as well. After the interrupt is enabled, the stack is not
full, and the external interrupt is active, a subroutine call
to location 04H or 08H occurs. The interrupt request flag
(EI0F or EI1F) and EMI bits are all cleared to disable
other interrupts.
The Comparator 0 output Interrupt is initialized by set-
ting the Comparator 0 output Interrupt request flag
(C0F; bit 6 of the INTC0), which is caused by a falling
edge transition of comparator 0 output. After the inter-
rupt is enabled, and the stack is not full, and the C0F bit
is set, a subroutine call to location 0CH occurs. The re-
lated interrupt request flag (C0F) is reset, and the EMI
bit is cleared to disable further maskable interrupts.
The internal Timer/Event Counter 0 interrupt is initial-
ized by setting the Timer/Event Counter 0 interrupt re-
quest flag (T0F;bit 4 of the INTC1), which is normally
caused by a timer overflow. After the interrupt is en-
abled, and the stack is not full, and the T0F bit is set, a
subroutine call to location 010H occurs. The related in-
terrupt request flag (T0F) is reset, and the EMI bit is
cleared to disable further interrupts. The Timer/Event
Counter 1 is operated in the same manner, The
Timer/Event Counter 1 related interrupt request flag is
T1F (bit 5 of the INTC1) and its subroutine call location
is 014H. The related interrupt request flag (T1F) will be
reset and the EMI bit cleared to disable further inter-
rupts.
Function
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 high-
est-order bit, or vice versa, otherwise OV is cleared.
PDF is cleared by system power-up or executing the
²CLR
WDT² instruction. PDF is set by exe-
cuting the
²HALT²
instruction.
TO is cleared by a system power-up or executing the
²CLR
WDT² or
²HALT²
instruction. TO is
set by a WDT time-out.
Unused bit, read as
²0²
Status (0AH) Register
Rev. 1.00
9
November 1, 2005
1
2
3
4
5
6, 7
AC
Z
OV
PDF
TO
¾
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
