Microsoft Word - Digital Logic Design v_4_6a

Open Collector/drain is useful for creating a wired “AND” by connecting the outputs together and
have one pull up resistor. This is also known as: Virtual AND, Dot-AND or Distributed AND.
Below are three points to consider in relation to this type of configuration:

• When all are high, then the pull up resistor provides the 1 output since all outputs are
  open


• If any one of the outputs go low then the output will short to ground and output is 0 (Logic
  AND)


• Symbols used to show the Wired-AND are shown below:

.

.

.

&

.

.

.

&

.

.

.

IEC International Symbols for the Function

.

.

.

IEC alternate

Symbol

IEEE alternate

Symbol

&

IC, TTL

GND

Internal

Output

Vo

Vcc

IC (MOS)

GND

Internal

Output

Drain

Collector

Pull up Resistor

required

Vo

Vcc

Pull up Resistor

required

Source

Gate

Is used to indicate an open collector or Drain output