Presettable synchronous 4-bit binary up/down counter

The 74HC191 is an asynchronously presettable 4-bit binary up/down counter. It contains four master/slave flip-flops with internal gating and steering logic to provide asynchronous preset and synchronous count-up and count-down operation. Asynchronous parallel load capability permits the counter to be preset to any desired value. Information present on the parallel data inputs (D0 to D3) is loaded into the counter and appears on the outputs when the parallel load (PL) input is LOW. This operation overrides the counting function. Counting is inhibited by a HIGH level on the count enable (CE) input. When CE is LOW internal state changes are initiated synchronously by the LOW-to-HIGH transition of the clock input. The up/down (U/D) input signal determines the direction of counting as indicated in the function table. The CE input may go LOW when the clock is in either state, however, the LOW-to-HIGH CE transition must occur only when the clock is HIGH. Also, the U/D input should be changed only when either CE or CP is HIGH. Overflow/underflow indications are provided by two types of outputs, the terminal count (TC) and ripple clock (RC). The TC output is normally LOW and goes HIGH when a circuit reaches zero in the count-down mode or reaches '15' in the count-up-mode. The TC output will remain HIGH until a state change occurs, either by counting or presetting, or until U/D is changed. Do not use the TC output as a clock signal because it is subject to decoding spikes. The TC signal is used internally to enable the RC output. When TC is HIGH and CE is LOW, the RC output follows the clock pulse (CP). This feature simplifies the design of multistage counters as shown in Fig. 5 and Fig. 6. In Fig. 5, each RC output is used as the clock input to the next higher stage. It is only necessary to inhibit the first stage to prevent counting in all stages, since a HIGH on CE inhibits the RC output pulse. The timing skew between state changes in the first and last stages is represented by the cumulative delay of the clock as it ripples through the preceding stages. This can be a disadvantage of this configuration in some applications. Fig. 6 shows a method of causing state changes to occur simultaneously in all stages. The RC outputs propagate the carry/borrow signals in ripple fashion and all clock inputs are driven in parallel. In this configuration the duration of the clock LOW state must be long enough to allow the negative-going edge of the carry/borrow signal to ripple through to the last stage before the clock goes HIGH. Since the RC output of any package goes HIGH shortly after its CP input goes HIGH there is no such restriction on the HIGH-state duration of the clock. In Fig. 7, the configuration shown avoids ripple delays and their associated restrictions. Combining the TC signals from all the preceding stages forms the CE input for a given stage. An enable must be included in each carry gate in order to inhibit counting. The TC output of a given stage it not affected by its own CE signal therefore the simple inhibit scheme of Fig. 5 and Fig. 6 does not apply. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC.

Orderable parts

Type number Orderable part number Ordering code (12NC) Package Buy from distributors
74HC191PW 74HC191PW,118 935188370118 SOT403-1 Order product
74HC191PW 74HC191PW,112 935188370112 SOT403-1 Order product


  • Complies with JEDEC standard no. 7A
  • CMOS input levels:
  • Synchronous reversible counting
  • Asynchronous parallel load
  • Count enable control for synchronous expansion
  • Single up/down control input
  • ESD protection:
    • HBM JESD22-A114F exceeds 2000 V
    • MM JESD22-A115-A exceeds 200 V
  • Specified from -40 °C to +85 °C and -40 °C to +125 °C

Target applications


Type numberProduct statusVCC (V)Output drive capability (mA)Logic switching levelstpd (ns)Power dissipation considerationsTamb (°C)Rth(j-a) (K/W)Ψth(j-top) (K/W)Rth(j-c) (K/W)Package name
74HC191PWProduction2.0 - 6.0± 5.2CMOS22low-40~1251021.028.6TSSOP16


Type numberOrderable part number, (Ordering code (12NC))StatusMarkingPackageOutline versionReflow-/Wave solderingPacking
( 9351 883 70118 )
Reel 13" Q1/T1

Quality, reliability & chemical content

Type numberOrderable part numberChemical contentRoHS / RHFEFRIFRMTBF (hour)MSLMSL leadfree
Quality and reliability disclaimer

Documentation (6)

File nameTitleTypeDate
74HC191Presettable synchronous 4-bit binary up/down counterData sheet2019-08-13
AN11044Pin FMEA 74HC/74HCT familyApplication note2019-01-09
HCT_USER_GUIDEHC/T User GuideUser manual1997-10-31
SSOP-TSSOP-VSO-WAVEFootprint for wave solderingWave soldering2009-10-08
SOT403-1_118TSSOP16; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or J Ordering code (12NC) ending 118Packing2013-04-08
SOT403-1plastic, thin shrink small outline package; 16 leads; 5 mm x 4.4 mm x 1.1 mm bodyOutline drawing2018-11-14


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Ordering, pricing & availability

Type numberOrderable part numberOrdering code (12NC)PackingBuy online
74HC191PW74HC191PW,118935188370118Reel 13" Q1/T1Order product
74HC191PW74HC191PW,112935188370112Bulk PackOrder product


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