Introduction / Context:
Classic TTL counters such as the 74192 (BCD up-/down-counter) provide terminal count outputs used for cascading or generating control pulses. Designers must know the active polarity to wire counters reliably in multi-decade chains.
Given Data / Assumptions:
- Device: 74192, BCD decade up-/down-counter with dedicated terminal count outputs (carry/borrow style).
- Terminal count outputs signal when the device is about to roll in the chosen direction.
- The outputs are used to trigger the next stage in a cascade.
Concept / Approach:
For the 74192, the terminal count outputs (often labeled CO and BO or similar) are active-LOW pulses indicating the counter has reached the limit in the up or down direction and is transitioning. Knowing the polarity ensures that cascade wiring correctly clocks or enables the adjacent stage without added inversion.
Step-by-Step Solution:
Identify function: terminal count provides a pulse at rollover/roll-under.Recall polarity: outputs go to the active level (LOW) at the terminal event.Implication: devices can be cascaded by feeding this low-active pulse appropriately to the next counter stage’s clock/enable line.Therefore, the statement about active-LOW behavior is correct.
Verification / Alternative check:
Check typical cascade examples in TTL counter datasheets where terminal lines interface directly without extra inverters due to active-LOW convention.
Why Other Options Are Wrong:
Incorrect / Only-up / Only-down: These contradict the standard active-LOW behavior reported for both terminal directions in BCD 74192 implementations.
Common Pitfalls:
Confusing 74192 with other counters (e.g., 74193 binary) that may label pins differently.Assuming active-HIGH based on generic “carry” naming; always verify polarity.
Final Answer:
Correct
Discussion & Comments