Saturday, July 5, 2014

Dexter components labeled

In case anyone is curious, here is a brief description of the integrated circuits on the board and their purpose.  I labeled these really quickly so they are a little hard to read.

  • Voltage converter: convert between 5V and 3.3V for I/O between 5V AVR and 3.3V raspberry pi.
  • micro 2: Auxilliary AVR microcontroller.  Injects frame number into video signal for PR-8210/A games.
  • sync separate: grabs vertical sync and horitzonal sync signals from video signal to that AVRs know when frame starts and which line number is active (so it can inject frame number into video signal)
  • video mux: so that video can be muted during seeks and frame number can be injected into video signal
  • tri-state buffer: to transform the centronics-24 connector so that it can support PR-8210A mode.  Also to squelch AUX AVR transmit (see OR gate 1).  The main AVR and aux AVR communicate with each other through TX/RX lines but the main AVR's TX/RX lines are also used to talk to the serial1/2 ICs so this is a way to shut down communication if the aux AVR is inactive without shutting the aux AVR down entirely (Warren pushed for this feature strongly.  I was okay with just putting the AUX AVR in reset mode when it was not being used)
  • OR gate 1: to squelch Auxilliary AVR's transmit line if either of the serial ICs are active (to avoid conflicts)
  • OR gate 2: to merge PR-8210A "remote control" and "remote control enable" signals into a single signal since we ran out of pins on the main AVR.  Also improves performance because it means code for main AVR uses less cycles.
  • micro 1: main AVR microcontroller, this is where the bulk of the work is done
  • BAT1/2: voltage protection in case someone plugs in a serial cable to the DB25 port to ensure that 12V/-12V doesn't make it to the 5V main AVR.  Also protects the optocoupler from some idiot plugging in something bad to the PR-8210 port.
  • RELAY: solid-state relay to add more protection to the main AVR
  • optocoupler: PR-8210 interface that protects the main AVR from someone plugging in something stupid to the PR-8210 port
  • serial 1/2: supports serial laserdisc players.  The reason there are two of these is that the Sony players are wired backward from the other players so we put two of these on the Dexter board so that the user doesn't have to mess around with null-modem adapters.
  • led driver: the board has a lot of LEDs on it and the main AVR can control them all using only 3 pins.  Efficient.

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