MOD-10 Counter Using IC 74LS90 (DECADE COUNTER)

Theory

A decade counter, utilizing the IC 7490, embodies a digital circuit designed to sequentially count through the decimal numbers 0 to 9 in binary form. The IC 7490, a 4-bit binary counter, plays a pivotal role in achieving this counting sequence

Binary Counting:

Let's delve into the detailed explanation of how a decade counter with the IC 7490 functions:

The IC 7490 operates in binary, counting in powers of 2.
It has four internal flip-flops, and its four outputs represent a binary number, ranging from 0000 to 1001 (0 to 9 in decimal).

Pin Configuration:

The IC 7490 has several pins, including A, B, C, D (BCD outputs), CLK (Clock Input), MR (Master Reset), and CPD (Count Down Enable).
The BCD outputs represent the binary-coded decimal equivalent of the current count.

Cascading Configuration:

To create a decade counter, multiple IC 7490s can be connected in a cascading configuration.
The carry-out (CO) and borrow-out (BO) pins facilitate the connection between ICs.
When the count reaches 9 and resets to 0, the CO pin generates a carry signal, enabling the next higher-order IC to increment its count.

Counting Sequence:

The counter advances its count on the rising edge of the clock signal applied to the CLK pin.
The counting sequence follows a decimal order: 0, 1, 2, ..., 9, and then resets to 0.

BCD Output:

The BCD outputs A, B, C, and D represent the binary-coded decimal equivalent of the current count.
These outputs can be used to drive external displays or other components that accept BCD input.

Clock Input:

The CLK pin is where an external clock signal is applied.
The counter increments its count on the rising edge of the clock signal.

Master Reset (MR) and Count Down Enable (CPD):

The MR pin allows for a synchronous reset of the counter to 0 when activated.
The CPD pin, when set, enables the count-down mode, allowing the counter to count in reverse order.

Modulo-10 Operation:

The IC 7490, configured as a decade counter, inherently performs a modulo-10 operation.
This ensures that the count sequence repeats after reaching 9, creating a decade counter.

Truth Table:

Applications:

Decade counters with the IC 7490 find applications in digital clock circuits, frequency dividers, and sequential control systems, where a count sequence from 0 to 9 is desired.