Re: Apple IIc DIN conversions and monitor troubles -- tech assistance requested

["Roger Johnstone" <rojaws@mac.com>]

In article <3c32a82b$0$1599$272ea4a1@news.execpc.com>, "nameless" 
<nospam@execpc.com> wrote:

> Hi everyone,
>
> i just spent a lengthy period of time perusing the FAQs, and while
> it did provide me with some helpful info, i'm afraid i'm still in the dark.
>
> First of all, i dug out my old Apple IIc and to my amazement i noticed
> that the 5-pin DIN ports in back for the printer and modem will take
> a MIDI cable.  So i fired her up, to see if there was something i could
> do to program these ports for MIDI.
>
> That's when i found out that my monitor isn't working so great.
> The whole image is skewed severely (i don't remember what direction),
> and since my monitor case was open already i poked around a bit
> at the degausser but that didn't seem to help at all.  However, wiggling
> around the RCA connection in the back of the Apple IIc didn't really
> help, but it gave more of a response than anything else.  So, i fear the
> RCA video jack could be shot.

I've got an old IIc like that too. The connector may have broken away from
the board, in which case it would need to be resoldered, or the contacts in
the socket may be bent out of shape.


> I was hoping I could plug the RCA out from my Apple into the
> Video In on my VCR to see if it looked ok on my TV, but i'm
> assuming that i can't do that (since reading the FAQ).
> Any ideas for a quick fix, besides trying to get my hands on an
> RF connector?

Yes, you can feed it into the video-in on a video recorder or TV. You only
need an RF modulator if you want to feed it in to the aerial connection.


> But really, i'm not too worried about the monitor thing, i'd really like
> to know more about the modem and printer ports, such as what their
> pinouts are, and more importantly, can i bypass the ROM to write
> my own drivers for them.  Luckily the middle pin is always the ground
> right?  Because that's just how the cable is made.  But it seemed like
> the rest of the pins needed to be rearranged a bit to make them
> run MIDI ok.
>
> I'm looking for some guidance here.
> Does anyone think it would be possible to write some simple
> assembly programs to control the data flow of the precise pins
> of these ports?
>
> any and all help is greatly appreciated.
>
> (i might forget to check back frequently, so please feel free
>  to CC any posts to me via e-mail.  my spam-retardant address is
>   mighty [underscore] joe [underscore] young [at] yifan [dot] net )
>
> thanks again.
>
> ~b
>
> ps.  i just read somewhere that the modem port is set to 300 baud,
> and the printer to 9600.  And although this source said something
> about changing settings with an Apple IIc System Utilities disk,
> i'm wondering if any of this can compensate for the difference between
> this 9600 baud and the MIDI standard of 31.25kbps??
>
> Is there anything that can be done about this?

No. While you can bypass the ROM routines the serial chip is still limited
to certain fixed speeds, the maximum is 19200 bits/s (or is it only 9600 on
a IIc?). It certainly can't do 31250 bits/s without a hardware modification
since the bit rate is derived by dividing a crystal-generated clock signal.

Also, for MIDI you should have an opto-isolator on the inputs which would
have to be in an external box.

Happy New Year!

--
Roger Johnstone, Invercargill, New Zealand
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Apple II - Future Cop:LAPD - iMac Game Wizard - WarCraft II
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