I have just burnt a set of Apple II Disk II PROM's P5A and P6A in two TBP28L22 PROM's.
Nothing special with the P6A PROM.
However here is a dump of the P5A PROM bin file as found in the Asimov repository.
When listing the PROM directly in the Apple II, you get the same bootstrap data.
But here is what you get when you read the PROM content directly with a programmer.
High data bits D4 to D7 are all reversed.
The programmer needs that bin file to program a correct P5 PROM.
A newly programmed TBP28L22 PROM programmed with that last bin file gives a controller working correctly .
Any idea or explanation about that issue?
Could it be that the high P5 data bits have been reversed in the Disk ][ controller PCB? Not yet investigated.
The original Apple II DISK II controller schematic does not explain that issue.
Of course, I did not burn the data as found in the file from the Asimov repository.
It looks like the Asimov P5A file had been created directly from the Apple II disassembler.
Yves
The Asimov dump is wrong. It was probably dumped while still installed on a Disk II Interface card with an Apple II program. I have succesfully recreated this card in VHDL and my P5 data is identical to your "PROM P5 READ DIRECTLY IN HILO ALL03".
In other words, the first one has its data scrambled like what can be seen on the Disk II Interface schematics, and your second one is a correct, straight dump from an isolated P5 ROM.
Hope this helps.
I checked my DiskII, and indeed the pins are reversed. It was probably for easier PCB routing.
AppleII - 6309
D0 - pin 6 Q1
D1 - pin 7 Q2
D2 - pin 8 Q3
D3 - pin 9 Q4
D4 - pin 14 Q8
D5 - pin 13 Q7
D6 - pin 12 Q6
D7 - pin 11 Q5
Thanks for that key information.
When you have to burn a one time programmable device, it's realy a critical information.
Yves
Thanks Gregor, for having taken the time to check the PCB routing
As mentioned above, when you have to burn a one time programmable device, it's realy a critical information to know beforehand.
Yves
In that case, it looks like the frequently published schematic contains an error.In that case, it looks like the frequently published schematic contains an error.
APPLE_DiskII_SCH_corect.jpg
Hi Gregor,
Thanks for that "patched" schematic".
In the meantime I have asked the Asimov repository webmaster to add the exact copy of the original P5A PROM content in the ad hoc folders.
Here is the bin file:
Apple Disk II 16 Sector Interface Card ROM P5 - 341-0027-exact-rom_dump-D4-D7 data bits swapped.zip
The other bin files could be used to program a 2716 or other EEPROM in a new design where the upper data bits are not swapped.
Yves