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SN74HC123 Dual Monostable

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by Ray

Dual retriggerable monostable multivibrator (one-shot) with reset, 74HC CMOS.

logicmonostableone-shotretriggerable74hctisoic-16
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SN74HC123

Texas Instruments · Monostable Multivibrator · SOIC-16

The SN74HC123 contains two retriggerable monostable multivibrators (one-shots). A trigger edge starts an output pulse whose width is set by an external resistor and capacitor, and a new trigger during the pulse retriggers (extends) it. Each has an active-low clear to end the pulse early. It is used for pulse generation, edge-to-pulse conversion, and timing.

Pinout

Pin Name Type Function
1 1A input Monostable 1 trailing-edge trigger input (active-low, Schmitt trigger). A high-to-low transition on 1A triggers the one-shot when 1B = H and 1R = H.
2 1B input Monostable 1 leading-edge trigger input (active-high, Schmitt trigger). A low-to-high transition on 1B triggers the one-shot when 1A = L and 1R = H.
3 1R input Monostable 1 reset input (active-low). Driving 1R low terminates the output pulse and holds 1Q = L, 1Q_bar = H. Must be tied high when unused.
4 1Q_bar output Monostable 1 inverted (complementary) buffered output. Drives 10 LSTTL loads (15 LSTTL as a bus driver) over the -55 to 125 C range.
5 2Q output Monostable 2 non-inverted buffered output. Pulse width tW = 0.45 * 2Rx * 2Cx at VCC = 5V.
6 2Cx passive Monostable 2 external timing capacitor terminal. Connect Cx from this pin to 2RxCx (pin 7); the capacitor sets the output pulse width together with 2Rx.
7 2RxCx passive Monostable 2 external Rx/Cx common node. Connect the external timing resistor from VCC to this pin and the timing capacitor between 2Cx (pin 6) and this pin. Minimum Rx ~5 kOhm, minimum Cx = 0 pF.
8 GND power_in Device ground reference (0 V).
9 2A input Monostable 2 trailing-edge trigger input (active-low, Schmitt trigger). A high-to-low transition on 2A triggers the one-shot when 2B = H and 2R = H.
10 2B input Monostable 2 leading-edge trigger input (active-high, Schmitt trigger). A low-to-high transition on 2B triggers the one-shot when 2A = L and 2R = H.
11 2R input Monostable 2 reset input (active-low). Driving 2R low terminates the output pulse and holds 2Q = L, 2Q_bar = H. Must be tied high when unused.
12 2Q_bar output Monostable 2 inverted (complementary) buffered output.
13 1Q output Monostable 1 non-inverted buffered output. Pulse width tW = 0.45 * 1Rx * 1Cx at VCC = 5V.
14 1Cx passive Monostable 1 external timing capacitor terminal. Connect Cx from this pin to 1RxCx (pin 15).
15 1RxCx passive Monostable 1 external Rx/Cx common node. Connect the external timing resistor from VCC to this pin and the timing capacitor between 1Cx (pin 14) and this pin.
16 VCC power_in Positive supply. HC types: 2 V to 6 V. HCT types: 4.5 V to 5.5 V. Absolute max 7 V.

Key specifications

Parameter Value
Type Dual retriggerable monostable (one-shot)
Logic family 74HC (CMOS)
Timing External R and C set pulse width
Retriggerable Yes, with clear input
Supply voltage 2 V to 6 V
Operating temperature -40 C to 85 C

Ordering variants

Same part, different packaging or reel option.

  • SN74HC123E
  • SN74HC123M
  • SN74HC123MT
  • SN74HC123M96
  • SN74HC123NSR
  • SN74HC123PW
  • SN74HC123PWR
  • SN74HC123PWT
  • SN74HC123F3A

CAD (KiCad official)

  • Symbol: sn74hc123.kicad_sym
  • Footprint: sn74hc123.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 (24 pp, sha256 1ae45a9eac40347d, 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