Re: Imagewriter II cable

[Rubywand <rubywand@swbell.net>]

william strutts writes ...
> 
> I have a cable I bought today at a Thrift store for an
> Imagewriter II to a IIe Super Serial card.  On the 25
> pin side, it has pins 2,3,6,7,8, and 20.  On one end
> there is an icon of a printer, this is the end with the
> mini-8 connector and the other has an Apple.  It is
> marked 590-0556-A.  Would this act as a null modem
> for a IIgs to Windows PC?  If so, will it support
> hardware handshaking?
 ....

     Sounds a lot like a Mac <--> IW-I cable. It seems like a good bet to work
as a IIgs <---> PC NULL modem cable. Probably, the 25-pin end is a male
connector; so, you would need a female <--> female adaptor to have a way to
plug the cable into a PC COM port.

     The absence of a connection to pin 5 on the Dsub-25 connector indicates
that the cable will, most likely, not support hardware handshaking between the
GS and PC. Exactly how important hardware handshaking may be for a GS <--> PC
connection remains unclear.

     About a month ago I ordered a Mac IW-1 Printer cable (950-0107) and a Mac
High-Speed Modem cable (950-0109) on-line from Radio Shack. (BTW, got very good
service; with regular postage, the cables arrive in a couple days.)  The idea
was to test performance of different transfer setups for sending files back and
forth between a IIgs and a PC.

     Mapping the lines for each cable showed that the IW-1 cable lacks the
connections to support hardware handshaking. The Mac High-Speed Modem cable
supports hardware handshaking. (It does not have the connection to support
RS-423 operation-- recommended for very long cables; but, that is probably not
important since the cable is just 10' long.)

     My usual cable is an Apple IIgs High-Speed Modem (as described in the
Spectrum manual and Modem Works manual).  It is identical to the Mac High-Speed
Modem cable with the addition of a line to support RS-423.

     The GS <--> PC connections I tried out were ...

o- Apple IIgs High-Speed Modem cable + NULL modem adaptor

o- Mac High-Speed Modem cable + NULL modem adaptor

o- Mac IW-1 Printer cable + female-female adaptor.


     The testing involved regular Z-modem file transfers with HyperTerm running
on a 233MHz PC and Spectrum running on the IIgs (ROM-01 with 4MB and 10MHz
ZipGSx accelerator).  For IW-1 cable tests, the PC port was set Xon/Xoff flow
control.

     It was something of a chap to find no difference in performance! Setting
hardware handshaking or software flow control made no difference with any of
the cables except for the IW-1 cable, which would not work at all with hardware
flow control.

     The only significant impact on transfer speed came from slowing down the
IIgs. With no acceleration, the GS could not maintain transfers above about 38k
baud. And, again, hardware or software flow control did not matter.

     Of course, these results relate to just GS <--> PC transfers running the
software mentioned. When it comes to selecting a cable which works well with
all sorts of telecom software, support for hardware flow control and having
other lines connected could make a big difference in results.



Rubywand