[BBC-Micro] 8MHz and 2MHz clocks on BBC Model B

James McGill plexer at gmail.com
Sun Oct 17 11:01:55 BST 2010


Hi all,

I'm trying to determine what the purpose of IC30 (74LS74) on the Model
B is. My best guess is that it should delay the 2MHz clock by 1/2 a
cycle (250nS), but it isn't clear to me that this would work unless
there was some skew between the 8MHz and 2MHz clock. If not, the
setup/hold times for IC30 would be violated (as it would be clocked at
the same time as the D input changed).

I'm wondering if anyone with a Model B and an oscilloscope would be
willing to probe the 8MHz and 2MHz clocks to confirm that such a skew
exists, and perhaps to measure it (or correct me if I'm totally wrong
about the purpose of IC30).

Regards,
James



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