Functionality: The 74LS90 is a 4-bit counter that counts in BCD from 0 to 9. It has four internal flip-flops, each representing a binary digit (0 to 9). The chip can count sequentially from 0 to 9 and then reset to 0, making it a decade counter.
Inputs and Outputs: The 74LS90 has four primary inputs:
- CLK (Clock): This is the input that triggers the counting operation on the rising edge (or falling edge, depending on the IC's version) of the clock signal.
- RST (Reset): When RST is LOW (logic 0), it resets the counter to 0.
- UP/DN (Up/Down): When UP/DN is LOW (logic 0), the counter counts upwards (0 to 9), and when it's HIGH (logic 1), it counts downwards (9 to 0).
- CN4 (Carry In): This input is used for cascading multiple 74LS90 ICs to create larger counters.
The chip has four BCD outputs (QD, QC, QB, QA) representing the current count, and a carry-out (CN4) output.
Decade Counting: The 74LS90 counts in a binary sequence that corresponds to the decimal numbers 0 to 9. The BCD outputs represent these decimal values in binary form.
Applications: The 74LS90 is commonly used in digital counters, timers, frequency dividers, and other applications where counting or sequencing is required. It's often used in conjunction with 7-segment displays to create digital counters.
Cascading: Multiple 74LS90 ICs can be cascaded together to create larger counters by connecting the carry-out (CN4) of one IC to the carry-in (CN4) of the next IC.
Power Supply: The IC typically operates on a 5V DC power supply.
Package: It is available in various package types, including DIP (Dual In-Line Package) and surface-mount variants.
