What is a three-state circuit?

Question

I have read the Wikipedia article Three-state logic, but it is not clear enough. What is a more simple explanation for what a three-state circuit is?

When and where do we use it? What has CMOS to do with three-state circuits?

http://electronics.stackexchange.com/questions/2443/tristate-a-pin — dext0rb, Sep 13 '13 at 20:50

score 20 · Accepted Answer · answered Sep 13 '13 at 20:52

Normal push-pull outputs drive the output either high or low by turning one of the output transistors on and the other off. Tri-state outputs can turn both transistors off, effectively cutting off the output completely. This allows another output on the same wire to drive it either high or low without creating a short circuit between chips.

Tri-state outputs can be implemented with either BJTs or MOSFETs, so there is no direct relation between them and CMOS.

score 0 · Answer 2 · answered Sep 17 '13 at 21:50

0

Tri-state may be considered as the high impedance state of a digital pin, wich was born to be 0 or 1

(ideally "0" = gnd = short circuit to the ground = very low impedance) ( "1" = 5V [ttl] = short circuit to vcc).

When you define a processor pin as an input, it usually become high impedance (tri state) to listen to the arriving data, may it be a button press or serial data, pulse, whatever.

answered Sep 17 '13 at 21:50

m33600

78
3

1

Actually trīstate refers to an **output**, with both N and P channel FETs turned off. – The Resistance Sep 20 '13 at 08:49

What is a three-state circuit?

2 Answers2