SN74HC42 BCD-to-Decimal Decoder

@@ -0,0 +1,64 @@+# SN74HC42++**Texas Instruments** · Decoder / Demultiplexer · SOIC-16++The SN74HC42 is a BCD-to-decimal decoder that takes a 4-bit BCD input and drives one of ten active-low outputs low, with invalid codes (10-15) leaving all outputs high. It is the 74HC-family equivalent of the classic 7442, used for 1-of-10 selection and display scanning.++## Pinout++| Pin | Name | Type | Function |+|---|---|---|---|+| 1 | Y0 | output | Active-LOW decoded output for BCD input 0000. LOW when A3:A0 = 0; otherwise HIGH. LSTTL fan-out: 10 loads. |+| 2 | Y1 | output | Active-LOW decoded output for BCD input 0001. |+| 3 | Y2 | output | Active-LOW decoded output for BCD input 0010. |+| 4 | Y3 | output | Active-LOW decoded output for BCD input 0011. |+| 5 | Y4 | output | Active-LOW decoded output for BCD input 0100. |+| 6 | Y5 | output | Active-LOW decoded output for BCD input 0101. |+| 7 | Y6 | output | Active-LOW decoded output for BCD input 0110. |+| 8 | GND | power_in | Ground reference (0 V). |+| 9 | Y7 | output | Active-LOW decoded output for BCD input 0111. |+| 10 | Y8 | output | Active-LOW decoded output for BCD input 1000. |+| 11 | Y9 | output | Active-LOW decoded output for BCD input 1001. |+| 12 | A3 | input | BCD address input, bit 3 (MSB). HC: VIH ≥ 3.15 V @ VCC=4.5 V; VIL ≤ 1.35 V. HCT: VIH ≥ 2 V, VIL ≤ 0.8 V @ VCC=4.5-5.5 V. Input leakage ≤ 1 µA. |+| 13 | A2 | input | BCD address input, bit 2. |+| 14 | A1 | input | BCD address input, bit 1. |+| 15 | A0 | input | BCD address input, bit 0 (LSB). |+| 16 | VCC | power_in | Positive supply. HC: 2-6 V. HCT: 4.5-5.5 V. Absolute max −0.5 V to 7 V. Quiescent ICC ≤ 8 µA typ (80 µA max over temp). |++## Key specifications++| Parameter | Value |+|---|---|+| Type | BCD-to-decimal (1-of-10) decoder |+| Logic family | 74HC (CMOS) |+| Outputs | 10, active-low |+| Supply voltage | 2 V to 6 V |+| Propagation delay | 20 ns typ at 5 V |+| Operating temperature | -40 C to 85 C |++## Ordering variants++- `SN74HC42CD74HC42M`+- `SN74HC42CD74HC42M.A`+- `SN74HC42CD74HC42E`+- `SN74HC42CD74HC42E.A`+- `SN74HC42CD74HCT42E`+- `SN74HC42CD74HCT42E.A`+- `SN74HC42CD54HC42F3A`+- `SN74HC42CD54HC42F3A.A`++## CAD (KiCad official)++- Symbol: `sn74hc42.kicad_sym`+- Footprint: `sn74hc42.kicad_mod`+- 3D model: SOIC-16 body from KiCad `Package_SO/SOIC-16_3.9x9.9mm_P1.27mm`.++## Provenance++Data extracted from the manufacturer datasheet, not a distributor listing:++- **Datasheet:** [Texas Instruments datasheet](https://www.ti.com/lit/ds/symlink/cd74hc42.pdf) (12 pp, sha256 `adc98c4caa771189`, retrieved 2026-08-17, tier: manufacturer)+- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.+- **CAD:** KiCad official libraries (CC-BY-SA 4.0).++[Datasheet PDF](docs/sn74hc42-datasheet.pdf)

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