HT68F20 datasheet(28/210 Pages) HOLTEK

28 / 210 page

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60

Rev. 1.00

November 3, 2009

· 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 high-

est-order bit but not a carry out of the highest-order bit,

or vice versa; otherwise OV is cleared.

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

²CLR WDT² instruction. PDF is set by executing 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.

In addition, on entering an interrupt sequence or execut-

ing a subroutine call, the status register will not be

pushed onto the stack automatically. If the contents of

the status registers are important and if the subroutine

can corrupt the status register, precautions must be

taken to correctly save it.

· STATUS Register

Bit

76543210

Name

¾¾

PDF

R/W

¾¾

R/W

POR

¾¾

xxxx

²x² unknown

Bit 7, 6

Unimplemented, read as

²0²

Bit 5

TO: Watchdog Time-Out flag

0: After power up or executing the

²CLR WDT² or ²HALT² instruction

1: A watchdog time-out occurred.

Bit 4

PDF: Power down flag

0: After power up or executing the

²CLR WDT² instruction

1: By executing the

²HALT² instruction

Bit 3

OV: Overflow flag

0: no overflow

1: an operation results in a carry into the highest-order bit but not a carry out of the

highest-order bit or vice versa.

Bit 2

Z: Zero flag

0: The result of an arithmetic or logical operation is not zero

1: The result of an arithmetic or logical operation is zero

Bit 1

AC: Auxiliary flag

0: no auxiliary carry

1: 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

Bit 0

C: Carry flag

0: no carry-out

1: an operation results in a carry during an addition operation or if a borrow does not take place

during a subtraction operation

C is also affected by a rotate through carry instruction.

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