The CD54/74HC190 are asynchronously presettable BCD decade counters, whereas the CD54/74HC191 and CD54/74HCT191 are asynchronously presettable binary counters.

Presetting the counter to the number on preset data inputs (A–D) is accomplished by a low asynchronous parallel load (LOAD)\ input. Counting occurs when LOAD\ is high, count enable (CTEN)\ is low, and the down/up (D/U) input is either high for down counting or low for up counting. The counter is decremented or incremented synchronously with the low-to-high transition of the clock.

When an overflow or underflow of the counter occurs, the MAX/MIN output, which is low during counting, goes high and remains high for one clock cycle. This output can be used for look-ahead carry in high-speed cascading (see Figure 1). The MAX/MIN output also initiates the ripple clock (RCO)\ output, which is normally high, goes low and remains low for the low-level portion of the clock pulse. These counters can be cascaded using RCO\ (see Figure 2).

If a decade counter is preset to an illegal state or assumes an illegal state when power is applied, it returns to the normal sequence in one or two counts, as shown in the state diagrams (see Figure 3).

• 2-V to 6-V VCC Operation (’HC190,191)
• 4.5-V to 5.5-V VCC Operation (’HCT191)
• Wide Operating Temperature Range of –55 to 125°C
• Synchronous Counting and Asynchronous Loading
• Two Outputs for n-Bit Cascading
• Look-Ahead Carry for High-Speed Counting
• Balanced Propagation Delay and Transition Times
• Standard Outputs Drive Up To 15 LS-TTL Loads
• Significant Power Reduction Compared to LS-TTL Logic ICs

• Function
• Counter
• Bits (#)
• 4
• Technology Family
• HC
• Supply voltage (Min) (V)
• 2
• Supply voltage (Max) (V)
• 6
• Input type
• Standard CMOS
• Output type
• Push-Pull
• Features
• Balanced outputs, High speed (tpd 10-50ns), Positive input clamp diode

CD74HC191的完整型号有：CD74HC191E、CD74HC191M、CD74HC191M96、CD74HC191MT，以下是这些产品的关键参数及官网采购报价：

CD74HC191E，工作温度：-55 to 125，封装：PDIP (N)-16，包装数量MPQ：25个，MSL 等级/回流焊峰值温度：N/A for Pkg Type，引脚镀层/焊球材料：NIPDAU，TI官网CD74HC191E的批量USD价格：.246（1000+）

CD74HC191M，工作温度：-55 to 125，封装：SOIC (D)-16，包装数量MPQ：40个，MSL 等级/回流焊峰值温度：Level-1-260C-UNLIM，引脚镀层/焊球材料：NIPDAU，TI官网CD74HC191M的批量USD价格：.417（1000+）

CD74HC191M96，工作温度：-55 to 125，封装：SOIC (D)-16，包装数量MPQ：2500个，MSL 等级/回流焊峰值温度：Level-1-260C-UNLIM，引脚镀层/焊球材料：NIPDAU，TI官网CD74HC191M96的批量USD价格：.217（1000+）

CD74HC191MT，工作温度：-55 to 125，封装：SOIC (D)-16，包装数量MPQ：250个，MSL 等级/回流焊峰值温度：Level-1-260C-UNLIM，引脚镀层/焊球材料：NIPDAU，TI官网CD74HC191MT的批量USD价格：.417（1000+）

14-24-LOGIC-EVM — 支持 14 到 24 引脚 PW、DB、D、DW、NS、DYY 和 DGV 封装的通用逻辑 EVM

该 EVM 设计用于支持采用 14 至 24 引脚 D、DW、DB、NS、PW、DYY 或 DGV 封装的任何逻辑器件。