© 2000 Scenix Semiconductor, Inc. All rights reserved. 33 SX User’s Manual Rev. 3.1 www.scenix.com Chapter 2 Architecture The individual bits of the STATUS register are described below. PA2:PA0 (Program Memory Page Selection Bits) PA2:PA0 are the program memory page selection bits. They are used to set the high-order bits of the
program counter for jump and call instructions. You can set them without affecting the other bits in the
STATUS register by using the “page” instruction. For details, see Section 2.6. T0 (Watchdog Timeout Bit) T0 is the Watchdog Timeout bit. It is set to 1 upon power-up and cleared to 0 when a watchdog timeout
occurs.  It  is  set  back  to  1  upon  execution  of  the  “clrwdt”  (clear  Watchdog  timer)  instruction  or
“SLEEP” instruction. For details, see Section 6.3. PD (Power Down Bit) PD is the Power Down bit. It is set to 1 upon power-up and cleared to 0 upon execution of the “SLEEP”
instruction. It is set back to 1 upon execution of the “clrwdt” (clear Watchdog timer) instruction. For
details, see Section 4.3. Z (Zero Bit) Z is the Zero bit. This bit is affected by the execution of many types of instructions (add, subtract,
increment, decrement, move, logic operations, and so on). When one of these instructions is executed,
the Z bit is set to 1 if the result is zero or cleared to 0 if the result is nonzero. DC (Digit Carry Bit) DC is the digit carry bit. This bit is affected by the execution of instructions that add or subtract. For
an instruction that performs addition, the C bit is set to 1 if a carry occurs out of bit 3 to bit 4, or is
cleared to 0 otherwise. For instructions that perform subtraction, the C bit is cleared to 0 if a borrow
occurs out of bit 3 to bit 4, or is set to 1 otherwise. This bit can be used to implement carry-bit functions
with single hexadecimal digits. C (Carry Bit) C is the carry bit. This bit is affected by the execution of the addition, subtraction, and rotate-through-
carry instructions. For an instruction that performs addition, the C bit is set to 1 if overflow occurs (a
carry out of bit 7), or is cleared to 0 otherwise. For an instruction that performs subtraction, the C bit
is cleared to 0 if underflow occurs (a borrow out of bit 7), or is set to 1 otherwise. The device can be configured either to use or not use the C bit as an implicit input to addition and
subtraction operations. This option is controlled by the CF bit in the FUSEX Word (a word that is
programmed at the same time as the program memory). An implicit addition of the C bit can be used
to implement multiple-byte addition and subtraction algorithms.