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The 'test pattern' of the Motorola MCM6830L7 ROM


Veteran Member
Jan 21, 2008
Western Norway
I recently got myself a MEK6800D1 I decided to get back up to working condition. After doing some research, I figured that the MIKBUG and MINIBUG portions of the ROM are well documented, but the Engineering Note 100 only lables the last 256 bytes of the ROM "Pattern Data", without ever mentioning it again.

The first challenge was to dump it, since the MCM6830 uses a pinout that predates the intel-style ROMs. At first I tried to read it out over serial, using MIKBUG. I later found out that A9 is permanently tied low, so this only gave me two copies of the MIKBUG portion of the ROM. The next thing I decided to try, was to use a patch-cable based ROM-adapter board with a programmer, and by using this I was able to read out the whole 1KB on the chip.

So what was this mysterious "pattern data"?... Well... I feel like there's a story behind this somewhere, but it turns out to to be what seems like an earlier version of MINIBUG assembled to start at $EE00 instead of $FE00. Why Motorola decided to use this as a filler, I have no idea, but I'd love to know if any of you have more info on how this came to be.

Right now I'm working out reconstructing an assembly listing of both versions, then I'll use git to get a diff. There are a few small differences on how and where some of the registers of the MC6850 are handled, but nothing major.
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