If the image you saw is like this one,
D7 imply bit positions in the status register, called
F (for flags) when part of the
AF register pair. The Ds are misleading because they imply some (nonexistent) relationship to the
D register or the data pins (which are multiplexed with the address lines and are actually called
Describing bit positions for the status flags doesn't mean much of anything for most people because the only instructions that operate on
F deal with a single bit at a time (conditional jumps, conditional subroutine calls and the instructions that set and clear the carry flag). The only way to operate on the flags as a whole would be to transfer them to or from another register by way of the stack.