SELMASK
ciab.prb |= (SELMASK(0)|SELMASK(1)|SELMASK(2)|SELMASK(3));
prb &= ~SELMASK(drive);
prb |= (SELMASK(0)|SELMASK(1)|SELMASK(2)|SELMASK(3));
SELECT(SELMASK(drive));
DESELECT(SELMASK(drive));
SELECT(SELMASK(drive));
DESELECT(SELMASK(drive));
SELECT(SELMASK(drive));
DESELECT(SELMASK(drive));