Issue link: https://resources.pcb.cadence.com/i/1180526
PSpice User Guide Digital device modeling October 2019 398 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. See Input/Output model on page 393 for more information. Note that if the values of DRVH and DRVL in the I/O model are different, it is possible for the 1 and 0 levels to have different strengths. This is useful for open-collector devices, where the 0 level is at a higher strength than the 1 level (which drives at the Z strength). Drive impedances which are higher than the value of DIGDRVZ are assigned the Z strength (0). Likewise, drive impedances lower than the value of DIGDRVF are assigned the forcing strength (63). Controlling overdrive During a simulation, the simulator uses only the strength range number (0-63) to compare the driving strength of outputs. The simulator allows you to control how much stronger an output must be before it overdrives the other outputs driving the same node. This is controlled with the configurable DIGOVRDRV option. By default, DIGOVRDRV is 3, meaning that the strength value assigned to an output must be at least 3 greater than all other drivers before it determines the level of the node. The accuracy of the DIGOVRDRV strength comparison is limited by the size of the strength range, DIGDRVZ through DIGDRVF. The default drive range of 2 ohms to 20,000 ohms gives strength ranges (DRVH) . . . Level 1 Strength DIGDRVF DIGDRVZ (DRVL) . . . . . . Level 0 Strength 63 0 Output Drive Output Strength DIGDRVF DIGDRVZ . . . 63 0 Output Drive Output Strength Figure 7-2 Level 1 and 0 strength determination. Higher Strength Higher Impedance