Status Register

The Status register contains information about the result of the most recently executed arithmetic or logic instruction. For details about the bits in this register and how they are affected by the different instructions, see the Instruction Set Summary.


Bit 7 – I: Global Interrupt Enable

Global Interrupt Enable

Writing a '1' to this bit enable interrupts on the device.

Writing a '0' to this bit disables interrupts on the device, independent of the individual interrupt enable settings of the peripherals.

This bit is not cleared by hardware after an interrupt has occurred.

This bit can be set and cleared by software with the SEI and CLI instructions.

Changing the I flag through the I/O-register result in a one-cycle wait state on the access.

Bit 6 – T: Bit Copy Storage

Bit Copy Storage

The bit copy instructions bit load (BLD) and bit store (BST) use the T bit as source or destination for the operated bit.

A bit from a register in the register file can be copied into this bit by the BST instruction, and this bit can be copied into a bit in a register in the register file by the BLD instruction.

Bit 5 – H: Half Carry Flag

Half Carry Flag

This bit indicates a half carry in some arithmetic operations. Half carry is useful in BCD arithmetic.

Bit 4 – S: Sign Bit, S = N ⊕ V

Sign Bit, S = N ⊕ V

The sign bit (S) is always an exclusive or (xor) between the negative flag (N) and the two’s complement overflow flag (V).

Bit 3 – V: Two’s Complement Overflow Flag

Two’s Complement Overflow Flag

The two’s complement overflow flag (V) supports two’s complement arithmetic.

Bit 2 – N: Negative Flag

Negative Flag

The negative flag (N) indicates a negative result in an arithmetic or logic operation.

Bit 1 – Z: Zero Flag

Zero Flag

The zero flag (Z) indicates a zero result in an arithmetic or logic operation.

Bit 0 – C: Carry Flag

Carry Flag

The carry flag (C) indicates a carry in an arithmetic or logic operation.