[Coco] Fwd: Disto 4-in-1 card manual

[Gene Heskett]

On Friday 19 January 2007 16:20, Mark Marlette wrote:
>Gene,
>
>On the 4n1 no high current bus drivers and NO TERMINATION!!!!
>
Humm, since scsi is an open collector system, most any ttl 7406 can pull 
them down, even with resistive terms on both ends of the cable, thats 
only about 42 mills per logic zero if both ends of the conductor were 
termed.  Its borderline, but most IC's will do it, warming up a bit of 
course.  And I must have a newer one as there is what appears to be a 10 
pin termpack right on the 34 pin header, I'd assume for the data bus 
since that would only be 8 terms.  For the control signals, I'd think the 
term could be left out and std ttl drivers allowed to furnish the logic 
ones in the slower control circuits.

One of the things Tony was up against was the limited power available from 
the cart port, so I don't imagine he put a term on anything that didn't 
need it, terms are hungry for power you know at 8+ mills per line 
terminated, which goes up to 21 mills per term and line at logic zero. 
That is 170 mills for the duration of a byte of $00 sent or received. With 
active terms sitting at 3.0 volts, that's 200 mills for the duration of 
that $00 bytes existence on the bus.  It will need good bypassing. But, 
with your much lower powered single chip design and active terms, your 
power budget isn't nearly so constrained so you can afford to 'do it 
right'.

>On the SCSIsys side the getstat wasn't present, there were many others.

I can't argue there, I don't think any of my stuff ever used a getstat 
against the scsi driver.  I used it frequently for other stuff, along 
with the setstat that matched though.

>Haven't used it since the TC^3 was up and running and using Boisy's
> drivers.
>
>SuperDriver is by far the best driver ever for the CoCo.

No doubt!

[...]

-- 
Cheers, Gene
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