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SN74HC240 Inverting Octal Buffer

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by Ray

Octal inverting buffer and line driver with 3-state outputs in two 4-bit banks.

logicbufferinvertingline-driver3-state74hctisoic-20
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SN74HC240

Texas Instruments · Buffer / Line Driver · SOIC-20

The SN74HC240 is an octal inverting buffer and line driver with 3-state outputs, arranged as two 4-bit groups each with its own active-low output-enable. Each output is the logical inverse of its input, useful for driving buses while inverting, or for isolating two nibble-wide buses.

Pinout

Pin Name Type Function
1 1OE input Active-low output enable for bank 1 (drives 1Y1-1Y4). Low = outputs active (inverted A data); high = outputs in high-impedance state.
2 1A1 input Bank-1 data input 1; drives inverted onto 1Y1 when 1OE is low.
3 2Y4 tri_state Bank-2 buffered output 4 (inverted 2A4). High-impedance when 2OE is high.
4 1A2 input Bank-1 data input 2; drives inverted onto 1Y2 when 1OE is low.
5 2Y3 tri_state Bank-2 buffered output 3 (inverted 2A3). High-impedance when 2OE is high.
6 1A3 input Bank-1 data input 3; drives inverted onto 1Y3 when 1OE is low.
7 2Y2 tri_state Bank-2 buffered output 2 (inverted 2A2). High-impedance when 2OE is high.
8 1A4 input Bank-1 data input 4; drives inverted onto 1Y4 when 1OE is low.
9 2Y1 tri_state Bank-2 buffered output 1 (inverted 2A1). High-impedance when 2OE is high.
10 GND power_in Ground reference (0 V).
11 2A1 input Bank-2 data input 1; drives inverted onto 2Y1 when 2OE is low.
12 1Y4 tri_state Bank-1 buffered output 4 (inverted 1A4). High-impedance when 1OE is high.
13 2A2 input Bank-2 data input 2; drives inverted onto 2Y2 when 2OE is low.
14 1Y3 tri_state Bank-1 buffered output 3 (inverted 1A3). High-impedance when 1OE is high.
15 2A3 input Bank-2 data input 3; drives inverted onto 2Y3 when 2OE is low.
16 1Y2 tri_state Bank-1 buffered output 2 (inverted 1A2). High-impedance when 1OE is high.
17 2A4 input Bank-2 data input 4; drives inverted onto 2Y4 when 2OE is low.
18 1Y1 tri_state Bank-1 buffered output 1 (inverted 1A1). High-impedance when 1OE is high.
19 2OE input Active-low output enable for bank 2 (drives 2Y1-2Y4). Low = outputs active (inverted A data); high = outputs in high-impedance state.
20 VCC power_in Positive supply, 2 V to 6 V recommended operating range.

Key specifications

Parameter Value
Type Octal inverting buffer / line driver, 3-state
Logic family 74HC (CMOS)
Configuration 8 inverting buffers, two 4-bit banks
Supply voltage 2 V to 6 V
Output current +-6 mA at VCC = 4.5 V
Propagation delay 11 ns typ at 5 V
Operating temperature -40 C to 85 C

Ordering variants

Same part, different packaging or reel option.

  • SN74HC240DW
  • SN74HC240DB
  • SN74HC240DGS
  • SN74HC240N
  • SN74HC240NS
  • SN74HC240PW
  • SN74HC240J
  • SN74HC240FK
  • SN74HC240W

CAD (KiCad official)

  • Symbol: sn74hc240.kicad_sym
  • Footprint: sn74hc240.kicad_mod
  • 3D model: SOIC-20 wide body from KiCad Package_SO/SOIC-20W_7.5x12.8mm_P1.27mm.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: Texas Instruments datasheet (35 pp, sha256 5d711e6c13cd01a1, 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