The 74LS90 integrated circuit is basically a MOD-10 decade counter that produces a BCD output code. The 74LS90 consists of four master-slave JK flip-flops internally connected to provide a MOD-2 (count-to-2) counter and a MOD-5 (count-to-5) counter.
The SN54/74LS90, SN54/74LS92 and SN54/74LS93 are high-speed 4-bit ripple type
counters partitioned into two sections.
Each counter has a divide-by-two section and either a divide-by-five (LS90), divide by-six (LS92) or divide-by-eight (LS93) section which are triggered by a HIGH-toLOW transition on the clock inputs. Each section can be used separately or tied
together (Q to CP) to form BCD, bi-quinary, modulo-12, or modulo-16 counters. All
of the counters have a 2-input gated Master Reset (Clear), and the LS90 also has a
2-input gated Master Set (Preset 9)