16 Mar
2000
16 Mar
'00
4:16 a.m.
--- Philip.Belben(a)powertech.co.uk wrote:
> The "serial" bus is actually a
bastardised implementation of the IEEE-488
> bus, which CBM had used on the PET series.
Caused, IIRC, by Tramiel who demanded of the engineers that the next computer
not use the same connectors because of a supplier shortage at some point in
the PET's past (dunno if it was the edge-connector end or the IEEE-488 end
that was hard to come by, but that's the story that's been circulating for
twenty years).
> Data is transferred serially (at 300 baud)
instead of in parallel, other
> than that I believe it's pretty much IEEE.
It is, effectively, the same character protocol, but the serial bus is
lacking in some of the handshaking lines that characterized the true IEEE-488.
There's a great book on the PET and its implementation of the IEEE-488 bus
by Osborne Press. If you ever see a copy of it at a bookstore or flea market
and have even considered programming for the PET, grab it.
Are you _sure_ it's 300 baud? I thought it was
2400. We had a 20K byte load
module that took about a minute to load - this corresponds to a little over
300 _bytes_ per second. Same load module from tape took SEVEN minutes! No
wonder speed loaders and things were popular! (Typical disk speed loader
used 2 of the wires in the serial bus for data, doubling the throughput. May
have used higher baud rate as well
It was because of this slowness that at one company, Software Productions,
we compressed the menu and splash screens for our C-64 version of "Micro
Mother Goose" (sold under the Reader's Digest label). It was a simple RLE
compression, but it cut the pictures down about 70% (lots of black space around
the menu items) and decreased the load times significantly even accounting for
the extra code to decompress the images. We had plenty of RAM and loads of
disk space, it was squished purely to speed up the load.
-ethan
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