SX User’s Manual Rev. 3.1 32 © 2000 Scenix Semiconductor, Inc. All rights reserved. www.scenix.com Chapter 2 Architecture For detailed information on program counter operation, see Section 2.6. 2.4.5 STATUS (Status Register) The STATUS register (address 03h) contains the device status bits, which are automatically set or
cleared by the device when certain events occur. The program can read this register at any time to
determine the status of the device. The format of the register is shown below, and Table 2-3 briefly
describes each of the register bit fields. The STATUS register is a read/write register except for the TO and PD bits, which are read-only bits.
Those two bits cannot be changed by writing to the STATUS register address. When you write to the STATUS register, it is recommended that you use the “setb” (set bit) and “clrb”
(clear bit) instructions to control the individual bits rather than “mov” (move) instructions to move
whole register values.  This  is because  the CPU often modifies the  STATUS register bits, possibly
resulting in register values that are different from what you expect. PA2 PA1 PA0 TO PD Z DC C Bit 7 Bit 0 Table 2-3  STATUS Register Bits Status Bits Description PA2:PA0 Program memory page selection bits. You set or clear these bits to specify the
program memory page number for a jump or call instruction. TO Watchdog timeout bit. This bit is set to 1 upon power-up and cleared to 0 when a
Watchdog timeout occurs. PD Power Down bit. This bit is set to 1 upon power-up and cleared to 0 when the
“SLEEP” instruction is executed. Z Zero bit. This bit is set when the result of an operation is zero. DC Digit Carry bit. This bit is set when there is a carry out from bit 3 to bit 4 in an
addition operation and cleared when there is a borrow out from bit 3 to bit 4 in a
subtraction operation. C Carry bit. This bit is set when there is a carry out of bit 7 in an addition operation
and cleared when there is a borrow out of bit 7 during a subtraction operation. It is
also affected by the rotate-through-carry instructions.