Re: ImageWriter II problems with a IIc

[dempson@actrix.gen.nz (David Empson)]

In article <2DC52D0A@mkt.eicon.com>, Jim Royal <jimr@EICON.COM> wrote:
> 
> I recently bought a secondhand ImageWriter II for my Apple IIc.  I'm having 
> problems getting it to print.
> 
> The printer is fine -- it works great when hooked up to my Macintosh.  But 
> when it is connected to the IIc, the print becomes garbled after a while. 
> When I dump a BASIC program listing, for example (via PR#1), the first page 
> is okay, but after that, characters drop out, lines are printed on top of 
> other lines, and the printout becomes unreadable.  AppleWorks does the same 
> thing.  Graphics printing is equally unreliable, and output is in 72 dpi 
> instead of 80 dpi (New Print Shop graphics extend off the edge of the page).

This is an obvious case of "no flow control".  The ImageWriter II has
a 2k print buffer, which will hold about a page of text (assuming
double spacing or shortish lines).  If the printer's buffer gets full,
it sends a signal to the computer telling the computer to wait and not
send any more data until the printer is ready (i.e. has a reasonable
amount of space in its buffer).  For some reason, the IIc is ignoring
this signal.

Locate the DIP switches in the ImageWriter.  Turn off the printer,
remove the cover, and manually move the print head to the right side.
You should see a couple of groups of switches on the left side.  One
group has eight switches, the other has six.

The group of eight is called switch bank 1, and the group of six is
switch bank 2.  The individual switches are numbered 1-1, through 1-8
and 2-1 through 2-6.

In short, find out what DIP switch 2-3 is set to.  In the OPEN
position (up), the ImageWriter II uses the DTR signal to tell the
computer to wait (hardware handshaking).  In the CLOSED position
(down), the ImageWriter II uses the XON/XOFF protocol: it sends a
character to the computer (Ctrl-S) telling it to stop, and another
character (Ctrl-Q) when it is ready to receive more data.

The UniDisk 3.5 version of the IIc does support the XON/XOFF protocol
(the original IIc doesn't), but the program has to enable it, which it
probably won't be doing.

It is much easier to just use DTR, since it is automatically supported
by the firmware.  Set switch 2-3 to the OPEN position and turn the
printer back on.

If the switch was already OPEN, then there might be something wrong
with your ImageWriter, or with the cable.

Check that the DTR signal is fed correctly through the cable.
DTR comes from pin 1 at the ImageWriter (bottom left corner when
looking at the plug) and should go to the DSR input of the IIc (pin 5,
which is the rightmost pin looking at the plug).

> The IIc is a UniDisk version with a Zip Chip. Printing is only slightly more 
> reliable with the accelerator off, but that might be an illusion.

No, you're not imagining things.  If the accelerator is off, the
computer can't generate data quite as fast, so the printer buffer will
overflow less often.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand