Re: upgrades for //c

[sbdocker@acs.ucalgary.ca (Sean Brendan Dockery)]

Stephen Buggie writes:

|>Regarding th    Regarding the IIc that works well with 1200 modem speed
|>but not with faster modems:
|>
|>I will be happy to swap my 1200 modem (US Robotics external) that works
|>great on my office IIc for your 2400 modem.  We will both end up with
|>"upgrades" that work fine with our respective computers!

Wayne Gretzky writes:

|My old //c at home as no trouble rnning my Zoom at 14.4 as long as HWHSK is
|off... seems weird that people would have problems above 1200b...

The modem port in a 1.023 MHz original IIc can handle speed upto and
including 9600 bps because of the limitation of the CPU speed.

The 1200 bps limitation that is continually being mentioned is with
regards to the built in port 2 firmware; it will only let you toggle
between 300 and 1200 bps.  (This is that dumb terminal you can get to
by typing "IN#2" following by "^AT" from the "]" prompt.)

Terminal programs which go directly to the hardware registers (on the
6551 chip) and handle all input via self-allocated interrupts do not
have this silly 1200 bps limitation.

In addition, accelerated systems can also go beyond the 9600 bps
limitation without losing characters because the CPU can reset the IRQ
flag much more quickly (because it can execute the interrupt servicing
code faster).

|mspaeth@magnusug.acs.ohio-state.edu  |_  ||  _|  / _ \/ _ \  Apple II Forever!
-- 
# internet: dockery@griffin.cuc.ab.ca   | Any  similarity  between the people
#      -or- sbdocker@acs.ucalgary.ca    | and ideas  mentioned in  the  above
#      -or- dockery@pro-calgary.cts.com | text and  those in existing fiction
# pro-line: dockery@pro-calgary         | or real life is purely coincidental