SN54/74LS90 • SN54/74LS92 • SN54/74LS93
FUNCTIONAL DESCRIPTION
The LS90, LS92, and LS93 are 4-bit ripple type Decade,
Divide-By-Twelve, and Binary Counters respectively. Each
device consists of four master/slave flip-flops which are
internally connected to provide a divide-by-two section and a
divide-by-five (LS90), divide-by-six (LS92), or divide-by-eight
(LS93) section. Each section has a separate clock input which
initiates state changes of the counter on the HIGH-to-LOW
clock transition. State changes of the Q outputs do not occur
simultaneously because of internal ripple delays. Therefore,
decoded output signals are subject to decoding spikes and
should not be used for clocks or strobes. The Q0 output of
each device is designed and specified to drive the rated
fan-out plus the CP1 input of the device.
A gated AND asynchronous Master Reset (MR1 • MR2) is
provided on all counters which overrides and clocks and
resets (clears) all the flip-flops. A gated AND asynchronous
Master Set (MS1 • MS2) is provided on the LS90 which
overrides the clocks and the MR inputs and sets the outputs to
nine (HLLH).
Since the output from the divide-by-two section is not
internally connected to the succeeding stages, the devices
may be operated in various counting modes.
LS90
A. BCD Decade (8421) Counter — The CP1 input must be ex-
ternally connected to the Q0 output. The CP0 input receives
the incoming count and a BCD count sequence is pro-
duced.
B. Symmetrical Bi-quinary Divide-By-Ten Counter — The Q3
output must be externally connected to the CP0 input. The
input count is then applied to the CP1 input and a divide-by-
ten square wave is obtained at output Q0.
C. Divide-By-Two and Divide-By-Five Counter — No external
interconnections are required. The first flip-flop is used as a
binary element for the divide-by-two function (CP0 as the
input and Q0 as the output). The CP1 input is used to obtain
binary divide-by-five operation at the Q3 output.
LS92
A. Modulo 12, Divide-By-Twelve Counter — The CP1 input
must be externally connected to the Q0 output. The CP0 in-
put receives the incoming count and Q3 produces a sym-
metrical divide-by-twelve square wave output.
B. Divide-By-Two and Divide-By-Six Counter —No external
interconnections are required. The first flip-flop is used as a
binary element for the divide-by-two function. The CP1 in-
put is used to obtain divide-by-three operation at the Q1
and Q2 outputs and divide-by-six operation at the Q3 out-
put.
LS93
A. 4-Bit Ripple Counter — The output Q0 must be externally
connected to input CP1. The input count pulses are applied
to input CP0. Simultaneous divisions of 2, 4, 8, and 16 are
performed at the Q0, Q1, Q2, and Q3 outputs as shown in
the truth table.
B. 3-Bit Ripple Counter— The input count pulses are applied
to input CP1. Simultaneous frequency divisions of 2, 4, and
8 are available at the Q1, Q2, and Q3 outputs. Independent
use of the first flip-flop is available if the reset function coin-
cides with reset of the 3-bit ripple-through counter.
FAST AND LS TTL DATA
5-92