Connecting TTL totem-pole outputs Complete the statement: Totem-pole outputs ________ be connected ________ because ________.

Introduction / Context:
TTL outputs often use a totem-pole (active pull-up and active pull-down) structure for fast transitions. Designers sometimes ask if two outputs can be tied together to increase current. With totem-pole outputs, this is unsafe.

Given Data / Assumptions:

• Both drivers are totem-pole TTL outputs.
• They may not be perfectly in phase or may drive opposite logic values.
• No explicit wired-OR capability is provided.

Concept / Approach:
Totem-pole outputs actively drive HIGH and LOW. If two are connected and one drives HIGH while the other drives LOW, a direct low-impedance path from VCC to GND is formed, causing large contention currents (shoot-through), potential overheating, and damage.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets warn against paralleling totem-pole outputs; contention graphs show current spikes when phases differ by even nanoseconds.

Why Other Options Are Wrong:

• Parallel for higher current (option a/d): Unsafe with totem-poles.
• Series for higher voltage (option c): Not a valid digital design technique and would violate VOH/VOL specs.

Common Pitfalls:
Confusing totem-pole with open-collector; only open-collector outputs may be safely wire-OR’d using external pull-ups.

Final Answer:
cannot, together, if the outputs are in opposite states excessively high currents can damage one or both devices