HT9480 Datasheet, PDF (12/57 Pages) Holtek Semiconductor Inc – Pager Controller

HT9480
Labels
C
AC
Z
OV
PD
TO
−
−
Bits
0
1
2
3
4
5
6
7
Function
C is set if the operation results in a carry out in addition or if a borrow does not
take place in subtraction; otherwise C is cleared. C is also affected by a rotate
through carry instructions.
AC is set if the operation results in a carry out of the low nibbles in addition or if
a borrow from the high nibble into the low nibble does not take place in
subtraction; otherwise AC is cleared.
Z is set if the result of an arithmetic or a logic operation is zero; otherwise Z is
cleared.
OV is set if the operation results in a carry into the high-order bit but not a carry
out of the high-order bit, or vice versa; otherwise OV is cleared.
PD is cleared during power up, and set by a “HALT” instruction.
TO is cleared during power up or by a “CLR WDT” instruction and a “HALT”
instruction. TO is set by a current timer time-out.
Undefined, read as “0”
Undefined, read as “0”
STATUS register
Interrupts
The HT9480 provides an internal programma-
ble timer interrupt, an internal data ready in-
terrupt, timer/event counter interrupt, and a
battery fail interrupt. The internal data ready
interrupt and the battery fail interrupt employ
the same jump location (04H). The interrupt
control register (INTC;0BH) contains interrupt
control bits to set not only the enable/disable
status but also the interrupt request flags.
Once an interrupt subroutine is serviced, the
other interrupts will all be blocked (by clearing
the EMI bit). This scheme may prevent any
further interrupt nesting. Other interrupt re-
quests may occur during this interval, but only
the interrupt request flag is recorded. If a cer-
tain interrupt requires servicing within the
service routine, the EMI bit and the correspond-
ing bit of the INTC register may be set to permit
interrupt nesting. When the stack is full, the
interrupt request will not be acknowledged
even if the related interrupt is enabled, until
the SP is decremented. If immediate service is
desired, the stack should be prevented from
becoming full.
All of these interrupts can support the wake-up
function. As an interrupt is serviced, a control
transfer occurs by pushing the contents of the
PC onto the stack, followed by a branch to a
subroutine at the specified location in the pro-
gram memory. Only the contents of the PC 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 desired control sequence, the con-
tents should be saved in advance.
The data ready interrupt and battery fail inter-
rupt share the same subroutine call location
04H. Checking the battery fail interrupt bit
(BF;bit 4 of 1EH) and the data ready interrupt
bit (DR; bit 7 of 1EH) can determine which kind
of interrupt has occurred. The value of 1EH-bit
7 DR is cleared “0” by the decoder data ready
interrupt signal, and is set to “1” when the µC
sets this bit high. Both interrupt bits are active
low.
The data ready interrupt is generated by the
pager decoder after a valid call is received, and
is initialized by setting the data ready interrupt
request flag (EIF; bit 4 of INTC) and the data
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23th Feb ’98