Global Standards for the Microelectronics Industry
output stage source power voltage or output stage ground reference (pin) (VSSQ; GNDQ)
The ground reference voltage for the data output (Q) or input/output (DQ) pins. Other, non-data, output transistors may also be designated to be referenced to this ground pin. Internal to the device, this pin shall be dc-isolated from the primary ground reference (VSS) pin and any other ground reference pin. External to the device, it must be dc‑common with the primary ground reference.
References:
JESD21-C, 1/97
