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PLCC 44 PROM programming with TL866

July 22, 2020
tags: ,

Even the retro world is moving away from the regular DIP packaging sometimes. The Atari Falcon, and third party ROM boards from Exxos, use the 27C4096 PROM in PLCC packaging to hold TOS (the operating system).

The TL866 with its DIP40 socket cannot obviously handle these, but a quick search shows us that there exists many adapter packages available to purchase that will sort out various types of popular socket formats. Including 44 pin PLCC.

However, the most common such adapter isn’t meant for PROMs, but for micro controllers (like the AT89C51 used for the example below). While the pin assignment is almost the same, for the critical purpose of programming the NC pins are swapped.


$ minipro -p AT27C4096@DIP40 -r test.bin
Found TL866A 03.2.86 (0x256)
Invalid Chip ID: expected 0x1E00F400, got 0xFFFFFFFF (unknown)
(use '-y' to continue anyway at your own risk)


If we want to program PROMs with this adapter, we need to perform a slight modification.


Comparing different PLCC44 pinouts


Simply, but carefully, bridge pins 12-13 and 33-34 on the PLCC adapter (not the DIP!) and off you go.


Pins bridged


$ minipro -p AT27C4096@DIP40 -w dualtos_swapped.img
Found TL866A 03.2.86 (0x256)

VPP=13.5V, VDD=6.5V, VCC=5V, Pulse=100us
Chip ID OK: 0x1E00F400
Writing Code... 77.79Sec OK
Reading Code... 5.58Sec OK
Verification OK


Happy programming.

3 Comments leave one →
  1. Zoli permalink
    November 22, 2020 17:35

    Hello why didnt u upload this on youtube? I Just found this after i did figure out :).

  2. August 13, 2021 17:11

    Hello, this was really helpful, had the adapter and the mod worked perfect, thank you!

  3. Alfa permalink
    October 31, 2021 23:11

    Just use two breadboard jumper wires and stick them between plcc legs and plcc socket. You can use some other thin wires…
    No soldering. Simple.

    Thank you, it was EXTREMELY HELPFUL!

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