Multiple Outputs from a General-Purpose CMOS Logic IC Come Into Conflict (Short-Circuiting)

Unlike diodes, the outputs of typical CMOS logic ICs cannot be wired-ORed together, except those with three-state outputs. Even in the case of CMOS logic ICs with three-state outputs, unintended current might flow, causing IC degradation, if they are enabled simultaneously. When creating a circuit design, ensure that multiple outputs will not be enabled at any given time. Also, the outputs of CMOS logic ICs without bushold become unstable if all of them are disabled (i.e., assume the High-Z state) without being pulled up to VCC or down to GND.

• For a description of logic transitions of three-state bus buffers, see the following FAQ entry.
  FAQ : Do bidirectional bus buffers have any constraints on the timing of the direction (DIR) and other input signals?
• For a description of bushold, see the following FAQ entry.
  FAQ : What is bushold?

Only the gates in the same package may be wired-ANDed to increase the drive capability (i.e., output current). However, it is recommended to use high-drive ICs (with an IO of ±24 mA) instead.

• For a description of high-drive CMOS /logic ICs, see the DC Characteristics table shown in the FAQ entry
  FAQ : How many amperes of current can an output pin drive?