Interfacing the $74$HCMOS to the $74$ALSTTL:

$74$HCMOS produces a maximum low level output of $0\mathrm{.}1$ V and $74$ALSTTL accepts any voltage up to $0\mathrm{.}8$ V as LOW level input, so there iswhen interfacing.

$74$HCMOS produces a minimum HIGH level output of $4\mathrm{.}9$ V and $74$ALSTTL accepts any voltage above $2\mathrm{.}0$ V as HIGH level input, so there iswhen interfacing.