P3 and P4 B row pins used for on VMIVME 2128
The VMIVME-2128 is capable of delivering 128 channels of high voltage and/or high current sink outputs. The VMIVME-2128 open collector output drivers are capable of supporting output voltages from 5 to 48 VDC.
The output driver user load return currents must be provided the lowest resistance return path possible to the user voltage supply. These return currents must not be allowed to flow through the VMEbus backplane digital ground return. They must flow back through the front panel connectors P3 and P4 B-row pins to the user supply, or through the P2 connector pins A1 through A26 if the P2 user ground option is ordered. If the user ground is of insufficient quality that the user load return currents flow onto the backplane digital ground, the fuse (F1) will blow and render the board inoperative. The function of this fuse is to protect the backplane digital ground pins, since they are not rated for the magnitude of user load currents this board is capable of handling. Blown fuses usually indicate poor user ground quality. The fuse circuit is necessary for digital input ground returns for control signals to the output driver. Refer to VMIVME 2128 product manual and specification for further technical information.