HT46R321 datasheet(10/45 Pages) HOLTEK

10 / 45 page

HT46R321

Rev. 1.00

August 3, 2007

Status Register

- STATUS

This 8-bit register contains the zero flag (Z), carry flag

(C), auxiliary carry flag (AC), overflow flag (OV), power

down flag (PDF), and watchdog time-out flag (TO). It

also records the status information and controls the op-

eration sequence.

With the exception of the TO and PDF flags, bits in

the status register can be altered by instructions like

most other registers. Any data written into the status

tion operations 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

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 provide an external interrupt, an internal

timer/event counter interrupt and an A/D converter inter-

rupt. The Interrupt Control Register, INTC, contains the

interrupt control bits to set the enable or 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 happen during this interval but

only the interrupt request flag is recorded. If a certain in-

terrupt requires servicing within the service routine, the

EMI bit and the corresponding bit in INTC may be set to

allow interrupt nesting. If the stack is full, the interrupt re-

quest will not be acknowledged, even if the related inter-

rupt is enabled, until the stack pointer is decremented. If

immediate service is desired, the stack must be pre-

vented from becoming full.

Bit No.

Label

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 ro-

tate through carry instruction.

1AC

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.

3OV

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

PDF is cleared by a system power-up or executing the

²CLR WDT² instruction. PDF is set by

executing the

²HALT² instruction.

5TO

TO is cleared by a system power-up or executing the

²CLR WDT² or ²HALT² instruction. TO

is set by a WDT time-out.

6, 7

Unused bit, read as

²0²

Status (0AH) Register

Bit No.

Label

Function

EMI

Controls the master (global) interrupt (1=enabled; 0=disabled)

EEI

Controls the external interrupt (1=enabled; 0=disabled)

ETI

Controls the Timer/Event Counter interrupt (1=enabled; 0=disabled)

EADI

Controls the A/D converter interrupt (1=enabled; 0=disabled)

EIF

External interrupt request flag (1=active; 0=inactive)

Internal Timer/Event Counter request flag (1=active; 0=inactive)

ADF

End of A/D conversion interrupt request flag (1=active; 0=inactive)

Unused bit, read as

²0²

INTC (0BH) Register

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