Controlling I/O Termination
This topic contains details about configuring I/O.
These termination techniques range from the weak resistive pull-up circuit, the p r keeper circuit ( also known as a “bus hold” circuit) and user-configurable ground pins. These termination features, where current, are controllable on either a per-pin or whole unit basis, with respect to the CPLD family members. Termination on I/O pins found in your design and termination on unused I/O pins are controlled separately.
Whenever a pad is perhaps not driven either externally or by the CPLD macrocell, the resistive pull-up circuit, if enabled, keeps a top logic state to stop the pad from floating. Whenever a low logic degree is placed on the pad, the pull-up continues to supply handful of present.
The keeper that is weak, if enabled, drives a weak 0 or 1 degree to match the amount it detects on the pad. Continue reading