74HC191 Presettable synchronous 4-bit binary up/down counter Rev. 5 13 August 2019 Product data sheet 1. General description 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 V . CC 2. Features and benefits 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 CNexperia 74HC191 Presettable synchronous 4-bit binary up/down counter 3. Ordering information Table 1. Ordering information Type number Package Temperature range Name Description Version 74HC191D -40 C to +125 C SO16 plastic small outline package 16 leads body width 3.9 mm SOT109-1 74HC191DB -40 C to +125 C SSOP16 plastic shrink small outline package 16 leads SOT338-1 body width 5.3 mm 74HC191PW -40 C to +125 C TSSOP16 plastic thin shrink small outline package 16 leads SOT403-1 body width 4.4 mm 4. Functional diagram 15 1 10 9 D0 D1 D2 D3 12 13 PL RC 11 13 TC RC U/D PARALLEL LOAD 5 15 D0 CIRCUIT 3 Q0 CE TC 4 12 1 D1 2 Q1 10 D2 6 Q2 D3 9 CP BINARY 7 14 Q3 COUNTER 11 PL U/D CE CP Q0 Q1 Q2 Q3 3 2 6 7 5 4 14 aaa-024376 aaa-024375 Fig. 1. Logic symbol Fig. 2. Functional diagram 5. Pinning information 5.1. Pinning 74HC191 D1 1 16 V 74HC191 CC 2 15 Q1 D0 D1 1 16 V CC Q0 3 14 CP Q1 2 15 D0 Q0 3 14 CP CE 4 13 RC CE 4 13 RC U/D 5 12 TC U/D 5 12 TC Q2 6 11 PL Q2 6 11 PL Q3 7 10 D2 7 10 Q3 D2 GND 8 9 D3 GND 8 9 D3 aaa-024378 aaa-024377 Fig. 4. Pin configuration SOT338-1 (SSOP16) Fig. 3. Pin configuration SOT109-1 (SO16) and SOT403-1 (TSSOP16) 74HC191 All information provided in this document is subject to legal disclaimers. Nexperia B.V. 2019. All rights reserved Product data sheet Rev. 5 13 August 2019 2 / 19