Schematics bug - Al!?

Juergen Buchmueller pullmoll at
Sat Jun 16 08:16:36 PDT 2007

This one dumbfound me:

In the AltoII schematics, disk controller, page 14 (DATA HANDLING) at the
top there is part #65 specified as 74155. This has to be wrong. It's a
74153, and in the AltoI schematics it is correct.

See e.g. for the pinouts of
the 74153 compared to the 74155. If the chip in the AltoII was really a
74155, it would not only be wire-disabled  (pin#1 = 1EN being tied to
ground), but also trying to read e.g. the bitclk from an input ;-)

I don't know if it would be wise to attach a page to the PDF listing the
known bugs?

BTW: I got the sector and word timing working so far that some data is read
into page 0! Unfortunately words are repeated once or twice, i.e. the
same word read multiple times by the DWT, and I think this is because I
have the bitclock too fast or completely wrong.

Said part #65 seems to be responsible for generating the bitclock, and I'm
currently trying to understand the pulse sequence it should generate.


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