Preliminary
HT48R06A-1
tions related to the status register may give
different results from those intended. The
TO flag can be affected only by system
power-up, a WDT time-out or executing the
"CLR WDT" or "HALT" instruction. The PD
flag can be affected only by executing the
"HALT" or "CLR WDT" instruction or a sys-
tem power-up.
the other interrupts will be blocked (by clearing
the EMI bit). This scheme may prevent any fur-
ther interrupt nesting. Other interrupt re-
quests may happen during this interval but
only the interrupt request flag is recorded. If a
certain interrupt requires servicing within the
service routine, the EMI bit and the correspond-
ing bit of INTC may be set to allow interrupt
nesting. If the stack is full, the interrupt request
will not be acknowledged, even if the related in-
terrupt is enabled, until the SP is decremented.
If immediate service is desired, the stack must
be prevented from becoming full.
The Z, OV, AC and C flags generally reflect the
status of the latest operations.
In addition, on entering the interrupt sequence
or executing the subroutine call, the status reg-
ister will not be pushed onto the stack automat-
ically. If the contents of the status are
important and if the subroutine can corrupt the
status register, precautions must be taken to
save it properly.
All these kinds of interrupts have a wake-up ca-
pability. As an interrupt is serviced, a control
transfer occurs by pushing the program counter
onto the stack, followed by a branch to a sub-
routine at specified location in the program
memory. Only the program counter is pushed
onto the stack. If the contents of the register or
status register (STATUS) are altered by the in-
terrupt service program which corrupts the de-
sired control sequence, the contents should be
saved in advance.
Interrupt
The device provides an external interrupt and
internal timer/event counter interrupts. The
Interrupt Control Register (INTC;0BH) con-
tains the interrupt control bits to set the en-
able/disable and the interrupt request flags.
External interrupts are triggered by a high to
low transition of INT and the related interrupt
Once an interrupt subroutine is serviced, all
Labels Bits
Function
C is set if the operation results in a carry during an addition operation or if a bor-
row does not take place during a subtraction operation; otherwise C is cleared. C
is also affected by a rotate through carry instruction.
0
1
C
AC is set if the 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.
AC
Z is set if the result of an arithmetic or logic operation is zero; otherwise Z is
cleared.
2
3
4
5
Z
OV is set if the 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.
OV
PD
TO
PD is cleared by system power-up or executing the "CLR WDT" instruction. PD
is set by executing the "HALT" instruction.
TO is cleared by system power-up or executing the "CLR WDT" or "HALT" in-
struction. TO is set by a WDT time-out.
6
7
Undefined, read as "0"
Undefined, read as "0"
¾
¾
Status register
10
February 25, 2000
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
