CY7C027V / CY7C028V / CY7C037V / CY7C038V Data Bus characteristics

Answer:

Questions:

- What would happen if we drive the unbuffered data lines while the device is not powered?

- Is it dangerous to drive the data bus when not in use?

Response:

These 3.3V dual-port RAMs have PFET output drivers. That means driving the data inputs with the device powered down will forward bias the PFET outputs, thereby supplying power to the output VCC bus. Driving the data inputs will essentially power the output power busses even if the device is powered down. This is inherently dangerous because you may accidently read or write from the memory without wanting to. This is NOT true for the equivalent 5V devices (CY7C027 / CY7C028 / CY7C037 / CY7C038).