Re: Apple II C start-up disc.

[Andrew Roughan <posty@203.triode.net.au>]

Randy Shackelford <shack@deimos.frii.com> wrote:
> In article <5im9qg$npu@uni.library.ucla.edu>,  <pubpc1@library.ucla.edu> wrote:

> [snip]

> >BJ, unless a //c has the earliest motherboard, which has a timing
> >defect, the port can drive a 14.4Kbaud modem fine.  You can also
> >hook up a faster than 14.4 modem, but the port speed is limited
> >to 19200, so you don't gain anything.

> Since //c's have no flow control, and the port goes from 9600 to 19200, 
> there is no way to run a 14400 at higher than 9600.

That's not strictly correct. Hopefully this will elaborate on the situation:

The 14.4k speed (or higher) is on the telephone line side of the modem.
The 19.2k speed is on the computer side of the modem.

I believe that all modems can successfully negotiate different speeds
on both sides. Therefore, the 14.4k modem will talk to the rest of the 
world quite happily at 14.4k while it talks to your //c at 19.2k.

If you have a //c which runs fast enough, then you should lose no characters
while the port is running at 19.2k, however, in practice, the standard //c 
will not keep up sufficiently at this speed.

There are no pins available for * Hardware * flow control, however the //c
can use XON/XOFF flow control with software which supports it. This may
allow a //c to keep up with 19.2k while you are not making heavy use
of the downlink....

However in practice for a reliable session you'd probably set the port speed
to 9600. The modem may try and negotiate 14.4k with the other side
but if it does you'll soon blow the modems internal buffer and lose
characters or even lose your connection with any kind of modem error
checking enabled.

Therefore you'll want to limit your 14.4k modem to 9600.

-- 
Andrew Roughan 				posty@triode.net.au
Apple II Sub-Editor, Applecations Magazine, Apple Users' Group, Sydney Oz!