74HC192D datasheet(2/13 Pages) PHILIPS

2 / 13 page

December 1990

Philips Semiconductors

Product speciﬁcation

Presettable synchronous BCD decade

up/down counter

74HC/HCT192

FEATURES

• Synchronous reversible counting

• Asynchronous parallel load

• Asynchronous reset

• Expandable without external logic

• Output capability: standard

• ICC category: MSI

GENERAL DESCRIPTION

The 74HC/HCT192 are high-speed Si-gate CMOS devices

and are pin compatible with low power Schottky TTL

(LSTTL). They are specified in compliance with JEDEC

standard no. 7A.

The 74HC/HCT192 are synchronous BCD up/down

counters. Separate up/down clocks, CPU and CPD

respectively, simplify operation. The outputs change state

synchronously with the LOW-to-HIGH transition of either

clock input. If the CPU clock is pulsed while CPD is held

HIGH, the device will count up. If the CPD clock is pulsed

while CPU is held HIGH, the device will count down. Only

one clock input can be held HIGH at any time, or

erroneous operation will result. The device can be cleared

at any time by the asynchronous master reset input (MR);

it may also be loaded in parallel by activating the

asynchronous parallel load input (PL).

The “192” contains four master-slave JK flip-flops with the

necessary steering logic to provide the asynchronous

reset, load, and synchronous count up and count down

functions.

Each flip-flop contains JK feedback from slave to master,

such that a LOW-to-HIGH transition on the CPD input will

decrease the count by one, while a similar transition on the

CPU input will advance the count by one.

One clock should be held HIGH while counting with the

other, otherwise the circuit will either count by two’s or not

at all, depending on the state of the first flip-flop, which

cannot toggle as long as either clock input is LOW.

Applications requiring reversible operation must make the

reversing decision while the activating clock is HIGH to

avoid erroneous counts.

The terminal count up (TCU) and terminal count down

(TCD) outputs are normally HIGH. When the circuit has

reached the maximum count state of 9, the next

HIGH-to-LOW transition of CPU will cause TCU to go LOW.

TCU will stay LOW until CPU goes HIGH again, duplicating

the count up clock.

Likewise, the TCD output will go LOW when the circuit is in

the zero state and the CPD goes LOW. The terminal count

outputs can be used as the clock input signals to the next

higher order circuit in a multistage counter, since they

duplicate the clock waveforms. Multistage counters will not

be fully synchronous, since there is a slight delay time

difference added for each stage that is added.

The counter may be preset by the asynchronous parallel

load capability of the circuit. Information present on the

parallel data inputs (D0 to D3) is loaded into the counter

and appears on the outputs (Q0 to Q3) regardless of the

conditions of the clock inputs when the parallel load (PL)

input is LOW. A HIGH level on the master reset (MR) input

will disable the parallel load gates, override both clock

inputs and set all outputs (Q0 to Q3) LOW. If one of the

clock inputs is LOW during and after a reset or load

operation, the next LOW-to-HIGH transition of that clock

will be interpreted as a legitimate signal and will be

counted.

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