Sega Master System / Mark III / Game Gear
f register consists of eight (semi-)independent bits which give you information about previous instructions' results. Not all instructions set all (or any) bits - see their individual documentation for more information.
1 if the result is negative (in two's complement representation),
0 otherwise. In other words, it's a copy of bit 7 (the high bit) of the result.
1 if the result is zero,
Simply a copy of bit 5 of the result, it's not very useful.
Simply a copy of bit 3 of the result, it's not very useful.
It's either the parity of the result (
1 if there is an even number of 1s in the binary representation of the result,
0 if odd); or it's the two's complement overflow (
1 if the operation caused the result to go past the -128/+127 limit,
1 if the last
daa-compatible instruction was a subtraction,
0 if it was an addition. It's used by the
daa instruction and isn't useful for much else.
1 if there was a carry into or out of the high bit of the result; in other words, if the operation caused the number to go past the 0/255 boundary.