Functional Description

The ’F161A and ’F163A count in modulo-16 binary se-

quence From state 15 (HHHH) they increment to state 0

(LLLL) The clock inputs of all flip-flops are driven in parallel

through a clock buffer Thus all changes of the Q outputs

(except due to Master Reset of the ’F161A) occur as a re-

sult of and synchronous with the LOW-to-HIGH transition

of the CP input signal The circuits have four fundamental

modes of operation in order of precedence asynchronous

reset (’F161A) synchronous reset (’F163A) parallel load

count-up and hold Five control inputsMaster Reset (MR

’F161A) Synchronous Reset (SR ’F163A) Parallel Enable

(PE) Count Enable Parallel (CEP) and Count Enable Trickle

(CET)determine the mode of operation as shown in the

Mode Select Table A LOW signal on MR overrides all other

inputs and asynchronously forces all outputs LOW A LOW

signal on SR overrides counting and parallel loading and

allows all outputs to go LOW on the next rising edge of CP

A LOW signal on PE overrides counting and allows informa-

flip-flops on the next rising edge of CP With PE and MR

(’F161A) or SR (’F163A) HIGH CEP and CET permit count-

ing when both are HIGH Conversely a LOW signal on ei-

ther CEP or CET inhibits counting

The ’F161A and ’F163A use D-type edge triggered flip-flops

and changing the SR PE CEP and CET inputs when the CP

is in either state does not cause errors provided that the

recommended setup and hold times with respect to the ris-

ing edge of CP are observed

The Terminal Count (TC) output is HIGH when CET is HIGH

and the counter is in state 15 To implement synchronous

multi-stage counters the TC outputs can be used with the

CEP and CET inputs in two different ways Please refer to

the ’F568 data sheet The TC output is subject to decoding

spikes due to internal race conditions and is therefore not

recommended for use as a clock or asynchronous reset for

flip-flops counters or registers

Mode Select Table

SR

PE

CET

CEP

Action on the Rising

Clock Edge (

L)

L

X

X

X

Reset (Clear)

H

L

X

X

H

H

H

H

Count (Increment)

H

H

L

X

No Change (Hold)

H

H

X

L

No Change (Hold)

For ’F163A only

State Diagram

TLF9486 – 5

3