Use negative logic for Front panel LEDs
All LEDs in the front panel, both TTL and INV TTL ones are positive logic:
- High level turns the LED ON.
- Low level turns the LED OFF.
It would be better to use negative logic just like in the CONV-TTL-BLO board.
Though this does not matter when LEDs are pulsing, this feature becomes desirable during startup.
- The TTL-BLO card has all LEDs ON immediately at power on (LED signals are Low), until they are switched off by the FPGA once it has finished configuration.
- On the TTl-RS485, they remain OFF, until the FPGA is configured.
This basically leaves the user for a few seconds without any feedback on whether the board is properly powered and functioning.