4 ms·
IEEE 1164, used for VHDL (VHSIC Hardware Description Language) has 9 distinct logic levels: 'U' uninitialized 'X' strong drive, unknown logic value '0' stron
by kurtisc 9y ago
IEEE 1164, used for VHDL (VHSIC Hardware Description Language) has 9 distinct logic levels:
'U' uninitialized
'X' strong drive, unknown logic value
'0' strong drive, logic zero
'1' strong drive, logic one
'Z' high impedance
'W' weak drive, unknown logic value
'L' weak drive, logic zero
'H' weak drive, logic one
'-' don't care
- masklinn 9y agoWhat does it mean by "drive", if you don't mind?
- rbalsdon 9y agoWeak drive means there’s a pull-up resistor and the port will drain itself. Strong drive means you’re going direct and the port won’t. Drive levels aside, this is called tri-state in electronics: https://en.m.wikipedia.org/wiki/Three-state_logic https://en.m.wikipedia.org/wiki/Three-state_logic
- dsr_ 9y agoThe strength of the signal, basically. You can implement default or fail-safe values by having a weak state and then overriding it with a strong drive.
- Symmetry 9y agoIn this case "drive" is short for "driver current," how much current is being used to direct the voltage in a particular way. For instance, in classic RTL you have fairly big resistors between power and all your outputs driving them weakly up. But you have NFET transistors that may or may not strongly drive your outputs down. So you've always got a 'H' leading into the outputs but sometimes also a '0'.