The ’HCT74 devices contain two independent
D-type positive-edge-triggered flip-flops. A low
level at the preset ( PRE) or
clear ( CLR) inputs sets or
resets the outputs, regardless of the levels of
the other inputs. When PRE
and CLR are inactive (high),
data at the data (D) input meeting the setup time
requirements are transferred to the outputs on the
positive-going edge of the clock (CLK) pulse.
Clock triggering occurs at a voltage level and is
not directly related to the rise time of CLK.
Following the hold-time interval, data at the D
input may be changed without affecting the levels
at the outputs.