Quartus® Prime Pro Edition User Guide: PCB Design Tools

ID 683768
Date 4/01/2024
Document Table of Contents Constant Definition

The constant definition block of the simulation file instantiates the voltage sources that controls the configuration modes of the I/O buffer.

Constant Definition Block

* Constant Definition
voeb oeb 0 vc * Set to 0 to enable buffer output
vopdrain opdrain 0 0 * Set to vc to enable open drain
vrambh rambh 0 0 * Set to vc to enable bus hold
vrpullup rpullup 0 0 * Set to vc to enable weak pullup
vpcdp5 rpcdp5 0 rp5 * Set the IO standard
vpcdp4 rpcdp4 0 rp4
vpcdp3 rpcdp3 0 rp3
vpcdp2 rpcdp2 0 rp2
vpcdp1 rpcdp1 0 rp1
vpcdp0 rpcdp0 0 rp0
vpcdn4 rpcdn4 0 rn4
vpcdn3 rpcdn3 0 rn3
vpcdn2 rpcdn2 0 rn2
vpcdn1 rpcdn1 0 rn1
vpcdn0 rpcdn0 0 rn0
vdin din 0 0


  • Voltage source voeb controls the output enable of the buffer and is set to disabled for inputs.
  • vopdrain controls the open drain mode for the I/O.
  • vrambh controls the bus hold circuitry in the I/O.
  • vrpullup controls the weak pullup.
  • The next 11 voltages sources control the I/O standard of the buffer and are configured through a later library call.
  • vdin is not used on input pins because it is the data pin for the output buffer.