- How is the Vcc/SMODE# pin used?
- What should I do with the SMODE pin?
- What is the difference between tying this pin to Vcc or ground?
In the CY7C42x5 and CY7C42x5V families of synchronous FIFOs, there is a pin labeled Vcc/SMODE# that is used to change the way the programmable flags work. If this particular pin is tied to Vcc, then the Almost Empty (PAE#) and Almost Full (PAF#) flags will respond asynchronously to a particular clock. If this pin is tied to ground, then the flag will respond synchronously to a clock edge which is why it is called SMODE = synchronous mode. Specifically, in SMODE, the Almost Empty flag will update after the next RCLK rising edge while the Almost Full flag will update after the next WCLK rising edge. Otherwise the Almost Empty flag will update a certain time after the last write operation and the Almost Full flag will update after the last read operation. Depending on how the external devices will react to the flag, there is an argument to using either mode. If comparing to other Cypress synchronous FIFOs (like the CY7C436xx family) this pin should be tied to ground. More recent synchronous FIFOs have synchronous mode only flags.