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Logic ICs
4 components in this category · Sourced from authorized channels · 24-hour quotes
Logic ICs are the building blocks of digital circuits — shift registers, counters, decoders, multiplexers and buffers that manipulate binary signals. Our most popular logic part is the 74HC595, an 8-bit serial-in/parallel-out shift register that lets a microcontroller drive hundreds of outputs using only three control lines. It is the standard solution for LED matrices, seven-segment displays, relay banks and any application where GPIO count is limited. We stock both SOP-16 surface-mount and DIP-16 through-hole variants from Nexperia and TI, with full electrical verification on every lot.
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Logic ICs – Frequently Asked Questions
How many 74HC595 can I cascade together?
Electrically you can chain dozens — the Q7' serial output of one feeds the DS input of the next. Practically, propagation delay accumulates at about 10 ns per stage, so a chain of 20 chips at 10 MHz shift clock will see the last chip lagging by 200 ns. For long chains, slow the clock or use dedicated LED drivers like MAX7219 or TLC5940.
74HC595 vs 74HCT595 — which should I use?
Same architecture and pinout. 74HC uses CMOS input thresholds that scale with Vcc; 74HCT uses fixed TTL thresholds (2 V high, 0.8 V low). Use HCT when interfacing to 5 V TTL logic in a mixed-voltage system; use HC when driving from CMOS outputs at 3.3 V or 5 V. For most modern MCU applications, HC is the right choice.
Can 74HC595 drive LEDs directly?
Yes, up to 25 mA per output pin, but total package current must stay under 50 mA. You can light 8 LEDs at 6 mA each with proper current-limiting resistors, or 2 LEDs at 25 mA. For higher-current displays, pair the 74HC595 with a ULN2003 Darlington array or use a dedicated LED driver.
What is the purpose of the MR (master reset) pin?
MR (pin 10, active-low) clears the internal shift register to all zeros. It does not affect the output latch. Tie it high (Vcc) if you don't need it. Useful for synchronizing multi-chip cascades at power-up or implementing a global blank function.
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