74HC193D,653

The 74HC193 and 74HCT193 are high-speed Si-gate CMOS devices and are pin compatible with Low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A. The 74HC193 and 74HCT193 are 4-bit synchronous binary up/down counters. Separate up/down clocks, CPU and CPD respectively, simplify operation. The outputs change state synchronously with the LOW-to-HIGH transition of either clock input. If the CPU clock is pulsed while CPD is held HIGH, the device will count up. If the CPD clock is pulsed while CPU is held HIGH, the device will count down. Only one clock input can be held HIGH at any time, or erroneous operation will result. The device can be cleared at any time by the asynchronous master reset input (MR); it may also be loaded in parallel by activating the asynchronous parallel load input (PL). The 74HC193 and 74HCT193 each contain four master-slave JK flip-flops with the necessary steering logic to provide the asynchronous reset, load, and synchronous count up and count down functions. Each flip-flop contains JK feedback from slave to master, such that a LOW-to-HIGH transition on the CPD input will decrease the count by one, while a similar transition on the CPU input will advance the count by one. One clock should be held HIGH while counting with the other, otherwise the circuit will either count by twos or not at all, depending on the state of the first flip-flop, which cannot toggle as long as either clock input is LOW. Applications requiring reversible operation must make the reversing decision while the activating clock is HIGH to avoid erroneous counts. The terminal count up (TCU) and terminal count down (TCD) outputs are normally HIGH.

• Synchronous reversible 4-bit binary counting
• Asynchronous parallel load
• Asynchronous reset
• Expandable without external logic