SN74AS169A - 同步 4 位加/减二进制计数器

SN74AS169A是TI德州仪器公司的一款计数器/算术/奇偶校验功能产品，SN74AS169A是同步 4 位加/减二进制计数器，本站介绍了SN74AS169A的封装应用图解、特点和优点、功能等，并给出了与SN74AS169A相关的TI元器件型号供参考。

SN74AS169A - 同步 4 位加/减二进制计数器 - 计数器/算术/奇偶校验功能 - 特殊逻辑 - 德州仪器

产品描述

These synchronous 4-bit up/down binary presettable counters feature an internal carry look-ahead circuitry for cascading in high-speed counting applications. Synchronous operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincident with each other when so instructed by the count-enable (, ) inputs and internal gating. This mode of operation eliminates the output counting spikes normally associated with asynchronous (ripple-clock) counters. A buffered clock (CLK) input triggers the four flip-flops on the rising (positive-going) edge of the clock waveform.

These counters are fully programmable; that is, they may be preset to either level. The load-input circuitry allows loading with the carry-enable output of cascaded counters. Because loading is synchronous, setting up a low level at the load (LOAD\) input disables the counter and causes the outputs to agree with the data inputs after the next clock pulse.

The internal carry look-ahead circuitry provides for cascading counters for n-bit synchronous application without additional gating. and inputs and a ripple-carry output () are instrumental in accomplishing this function. Both and must be low to count. The direction of the count is determined by the level of the up/down (U/D\) input. When U/D\ is high, the counter counts up; when low, it counts down. is fed forward to enable . , thus enabled, produces a low-level pulse while the count is zero (all inputs low) counting down or maximum (15) counting up. This low-level overflow ripple-carry pulse can be used to enable successive cascaded stages. Transitions at or are allowed regardless of the level of the clock input. All inputs are diode clamped to minimize transmission-line effects, thereby simplifying system design.

These counters feature a fully independent clock circuit. Changes at control inputs (, , , or U/D\) that modify the operating mode have no effect on the contents of the counter until clocking occurs. The function of the counter (whether enabled, disabled, loading, or counting) is dictated solely by the conditions meeting the stable setup and hold times.

The SN54ALS169B and SN54AS169A are characterized for operation over the full military temperature range of -55°C to 125°C. The SN74ALS169B and SN74AS169A are characterized for operation from 0°C to 70°C.

产品特性

Fully Synchronous Operation for Counting and Programming
Internal Carry Look-Ahead Circuitry for Fast Counting
Carry Output for n-Bit Cascading
Fully Independent Clock Circuit
Package Options Include Plastic Small-Outline (D) Packages, Ceramic Chip Carriers (FK), and Standard Plastic (N) and Ceramic (J) 300-mil DIPs

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