These synchronous presettable counters feature an internal carry look-ahead for cascading in high-speed counting applications. The 'LS668 are decade counters and the 'LS669 are 4-bit binary counters. 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 helps eliminate the output counting spikes that are normally associated with asynchronous (ripple-clock) counters. A buffered clock input triggers the four master-slave flip-flops on the rising (positive-going) edge of the clock waveform.

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

The carry look-ahead circuitry provides for cascading counters for n-bit synchronous applications without additional gating. Instrumental in accomplishing this function are two count-enable inputs and a carry output. Both count enable inputs (P\ and T\) must be low to count. The direction of the count is determined by the level of the up/down input. When the input is high, the counter counts up; when low, it counts down. Input T\ is fed forward to enable the carry output. The carry output thus enabled will produce a low-level output pulse when the count is maximum counting up or zero counting down. This low-level overflow carry pulse can be used to enable successive cascaded stages. Transitions at the enable P\ or T\ inputs 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 (enable P\, enable T\, load, up/down) that will modify the operating mode have no effect until clocking occurs. The function of the counter (whether enabled, disabled, loading, or counting) will be dictated solely by the conditions meeting the stable setup and hold times.

The 'LS668 and 'LS669 are completely new designs. Compared to the original 'LS168 and 'LS169, they feature 0-nanosecond minimum hold time, reduced input currents IIH and IIL, and all buffered outputs.

'LS668 …SYNCHRONOUS UP/DOWN DECADE COUNTERS 'LS669 …SYNCHRONOUS UP/DOWN BINARY COUNTERS

Programmable Look-Ahead Up/Down Binary/Decade Counters

• Fully Synchronous Operation for Counting and Programming
• Internal Look-Ahead for Fast Counting
• Carry Output for n-Bit Cascading
• Fully Independent Clock Circuit
• Buffered Outputs

• SN75LBC180 - 低功耗差动线路驱动器和接收器对
• TPS61071 - 采用小型 SOT-23 封装的可调节 600mA 开关式 90% 效率 PWM 升压转换器
• MSP430G2233 - MSP430G2x33、MSP430G2x03 混合信号微处理器
• SN74LVC3G07-Q1 - 具有漏极开路的汽车类三路缓冲器/驱动器
• TPA6011A4 - 具有音量控制和立体声耳机驱动的立体声 AB 类音频放大器
• DS90LV032A - 3V LVDS 四路 CMOS 差动线路接收器
• TS3A24157 - 0.65Ω 双路 SPDT 模拟开关、双通道 2:1 多路复用器/多路解复用器
• LM4132-Q1 - 汽车类 SOT23 精密低压降电压基准
• ADS6123 - 具有可选并行 CMOS 或 LVDS 输出的低功耗 12 位 80MSPS ADC
• UC2843AQ - 汽车类电流模式 PWM 控制器