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From: AgentFriday on 25 Mar 2010 04:32
On Mar 24, George <gh424NO824SPAM(a)cox.net> wrote:

> But I still would suspect things aren't set
>up right using the stock routines ...

Possible. We were powering the MAX circuit with the +5
line on the user port. That's all I can think of.

Maybe if I get ambitious I'll pull my 1MHz scope out of
the garage and see if I can remember how to use it.
Probably the only way to know for sure.

Hmmm... then there's that old idea of mine to use the
64 as a digital oscilloscope. (Digital as in, you only get
two levels.) Wonder if anyone's written that one yet.


AgentFriday
<my_nic_here(a)hotmail.com>
From: Groepaz on 25 Mar 2010 06:45
George wrote:

> Yes, the problem is described in item 4 on page 63 of the
> article. Basically, the problem occurs when Timer B
> underflows at about the same time as the interrupt register
> is read. So if something else, like Timer A, has actually
> generated the interrupt, but Timer B then times out just
> before you read the register, the flag for Timer B isn't
> set.
>
> The solution is to read the high byte of Timer B just
> before you read the interrupt register, and then again
> after, If the value is higher on the second read, then
> Timer B must have underflowed.
>
> This would not normally be a problem unless you are
> transmitting and receiving at the same time in full duplex.

interesting.. didnt know this

--

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Wenn man nicht so gut schwimmen kann, sollte man einfach nicht so weit ins
tiefe Wasser gehen.
<Bob Marley>


From: Jim Brain on 25 Mar 2010 13:23
On 3/25/2010 3:24 AM, AgentFriday wrote:
> On Wed, 24 Mar 2010 13:34:04 -0700 (PDT), christianlott1
>>
>
>> on an rs232 cart of jim brains design.
>
> I assume it was a basic transciever circuit that plugged
> into the user port?

No, there are two different designs. One is a "level shifter" that
plugs into the user port. Max speed is 2400-9600, depending on machine
and whether special UP9600 routines are in use.

The other is a 6551 cartridge, which adds a 6551 ACIA to the expansion
port. Custom routines are required, and top speed is 230Kbps

Jim
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