Aperture Controls

Cobb Accessport Reverse Engineering

Thanks to COVID, I had a lot of free time on my hands all of the sudden. I had this Accessport lying around that I couldn't use anymore so to keep my brain occupied I decided to see how it worked.

The Hardware

Accessport Disassembled

The unit comes apart with four screws hidden under the removable front cover. The rest of the components just "lay" inside the case. If you take apart your own unit, take care with the small plastic button that likes to fall out.

Accessport mainboard (Rear)

This is the back of the Accessport mainboard. The parts I could identify are:
  • LCD Display - Microtips Technology UMOH-8061MD-T
  • U7 Bus Processor: Microchip PIC32MX775F256H
  • U23 Main Processor: Freescale i.MX283 Multimedia Processor
  • U9 Memory: Micron 2Gb NAND Flash 29F2G08ABAEA
  • U24 Memory: Micron 1Gb DDR2 MT47H64M16HR-25E IT?
  • U19 Logic: 74LV123 Dual retriggerable monostable multivibrator with reset
  • (TI Chip near R61) Interface: Texas Instruments SN65HVD232 3.3V CAN Bus Transceiver
  • U14 Logic: Texas Instruments SN74LVC14A Hex Schmitt-Trigger Inverters
  • U1 Power: Texas Instruments TPS54140A Step Down DC/DC Converter
  • U17: Analog Devices AD5161 Digital Potentiometer
  • J3: Debug port for the PIC32 MCU
    • Pin 2 = VCC
    • Pin 4 = CLOCK
    • Pin 6 = DATA
    • Pin 8 = GND
  • J4: Currently can't find my notes on this port

Accessport mainboard (Front)

  • U12: An RGB LED or some kind of light sensor. I'm leaning towards LED
  • J6: Serial port connected to the main processor. 115200 Baud, 8 Data/1 Stop/No Parity

  • From the perspective of holding the AP like you normally would, USB connector at top left:
    • Pin upper right: Serial RX
    • Pin lower right: Serial TX
    • Pin center top: Ground
The bit ordering over serial is LSB. When you boot the AP, the serial line will spit out HTLLLLFLC where the number of L's is variable. If the flash chip is removed the serial stream will show 0x80508002, which is the error ERROR_ROM_NAND_DRIVER_NO_FCB ("Unable to find FCB") from the Freescale bootloader.

Next: Flash Chip