Motorola MC74AC190D, MC74AC190N Datasheet

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FACT DATA

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The MC74AC190 is a reversible BCD (8421) decade counter which features synchronous counting and asynchronous presetting. The preset feature allows the MC74AC190 to be used in programmable dividers. The Count Enable input, the Terminal Count output and the Ripple Clock output make possible a variety of methods of implementing multistage counters. In the counting modes, state changes are initiated by the rising edge of the clock.

• High-Speed — 120 MHz Typical Count Frequency

• Synchronous Counting

• Asynchronous Parallel Load

• Cascadable

• Outputs Source/Sink 24 mA

1516 14 13 12 11 10

21 3 4 5 6 7

P0CP RC

TC PL P2P

P1Q1Q0CE

U/D Q2Q3GND

PIN NAMES

Count Enable Input CP Clock Pulse Input P0–P3Parallel Data Inputs PL

Asynchronous Parallel Load Input U

/D Up/Down Count Control Input Q0–Q3Flip-Flop Outputs RC

Ripple Clock Output

TC Terminal Count Output



UP/DOWN COUNTER

WITH PRESET

AND RIPPLE CLOCK

N SUFFIX

CASE 648-08

PLASTIC

D SUFFIX

CASE 751B-05

PLASTIC

LOGIC SYMBOL

PL P0P1P2P

RC TC

CE CP

Q0Q1Q2Q

MC74AC190

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FACT DATA

FUNCTIONAL DESCRIPTION

The MC74AC190 is a synchronous up/down BCD decade counter. It contains four edge-triggered flip-flops with internal gating and steering logic to provide individual preset, count-up and count-down operations.

Each circuit has an asynchronous parallel load capability permitting the counter to be preset to any desired number. When the Parallel Load (PL

) input is LOW, information present on the Parallel Load inputs (P0–P3) is loaded into the counter and appears on the Q outputs. This operation overrides the counting functions, as indicated in the Mode Select Table.

A HIGH signal on the CE

input inhibits counting. When CE is LOW, internal state changes are initiated synchronously by the LOW-to-HIGH transition of the clock input. The direction of counting is determined by the U

/D input signal, as indicated in

the Mode Select Table. CE

and U/D can be changed with the clock in either state, provided only that the recommended setup and hold times are observed.

Two types of outputs are provided as overflow/underflow indicators. The terminal count (TC) output is normally LOW. It goes HIGH when the circuits reach zero in the count down mode or 9 in the count up mode. The TC output will then remain HIGH until a state change occurs, whether by counting or presetting or until U

/D is changed. The TC output should not be used as a clock signal because it is subject to decoding spikes.

The TC signal is also used internally to enable the Ripple

Clock (RC

) output. The RC output is normally HIGH. When CE is LOW and TC is HIGH, RC output will go LOW when the clock next goes LOW and will stay LOW until the clock goes HIGH again. This feature simplifies the design of multistage counters, as indicated in Figures a and b. In Figure a, each RC output is used as the clock input for the next higher stage. This configuration is particularly advantageous when the clock source has a limited drive capability, since it drives only the first stage. To prevent counting in all stages it is only necessary to inhibit the first stage, since a HIGH signal on CE

inhibits the

output pulse, as indicated in the RC Truth Table. A disadvantage of this configuration, in some applications, is the timing skew between state changes in the first and lost stages. This represents the cumulative delay of the clock as it ripples through the preceding stages.

A method of causing state changes to occur simultaneously in all stages is shown in Figure b. All clock inputs are driven in parallel and the RC

outputs propagate the carry/borrow signals in ripple fashion. In this configuration the LOW state duration of the clock must be long enough to allow the negative-going edge of the carry/borrow signal to ripple through to the last stage before the clock goes HIGH. There is no such restriction on the HIGH state duration of the clock, since the RC

output of any device goes HIGH shortly after its

CP input goes HIGH.

The configuration shown in Figure c avoids ripple delays

and their associated restrictions. The CE

input for a given stage is formed by combining the TC signals from all the preceding stages. Note that in order to inhibit counting an enable signal must be included in each carry gate. The simple inhibit scheme of Figures a and b doesn’t apply, because the TC output of a given stage is not affected by its own CE

MODE SELECT TABLE

Inputs

PL CE U/D CP

Mode

H L L Count Up H L H Count Down

L X X X Preset (Asyn.)

H H X X No Change (Hold)

RC TRUTH TABLE

Inputs Output

PL CE TC* CP RC

H L H H H X X H

H X L X H

L X X X H

*TC is generated internally H = HIGH Voltage Level L = LOW Voltage Level X = Immaterial = LOW-to-HIGH Transition

COUNT UP COUNT DOWN

0 1 2 3 4

12 11 10 9

STATE DIAGRAM

MC74AC190

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FACT DATA

Figure a: N-Stage Counter Using Ripple Clock

Figure b: Synchronous N-Stage Counter Using Ripple Carry/Borrow

Figure c: Synchronous N-Stage Counter With Parallel Gated Carry/Borrow

DIRECTION

CONTROL

CLOCK

ENABLE

U/D CE CP

RC U/D

CE CP

RC U/D

CE CP

U/D CE CP

RC U/D

CE CP

RC U/D

CE CP

DIRECTION

CONTROL

CLOCK

ENABLE

U/D CE CP TC

DIRECTION

CONTROL

CLOCK

ENABLE

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