From: derosa@rtsg.mot.com (John DeRosa)
Subject: V.32bis High Speed Modem Cabling - Long Discussion
Summary: what is the proper cable for a high speed modem?
Keywords: high speed modem v.32bis serial cable
Reply-To: motcid!derosa@uunet.uu.net
Organization: Motorola Inc., Cellular Infrastructure Group
Date: Mon, 12 Oct 1992 02:23:35 GMT

NOTE: If your last name starts with a "D", please 
reply to this posting, I am unsure if this is getting out.
The "D" thing is to eliminate too many mailers back to me.

2nd NOTE:  This is a fairly long posting on RS-232 Modems
cabling.  Sorry but I wanted to be complete.

I have been working around the clock to try and figure
out what cable will work between a Macintosh and any of 
a number of brands of modems.

My problem first started when I purchased a new
Hayes Ultra 144 that does V.32bis.  I could not
get it to talk at 14.4K.  In fact I could only get
it to talk at 2400.  I first called the Hayes support
line at 404-441-1617.  A semi-friendly technitian 
told me that I needed at least (DB25 <-> DIN8)
pin 4 <-> 1 and pin 5 <-> 2 and said goodbye.

I subsequently called up the Hayes BBS at 
1-800-874-2937 and searching their tech support 
data base came up with the following pin out
for a full hardware handshaking cable;

DB25 <-> DIN8
=============
4	1
5	2
2	3               Read more below
1,7	4		as this pinout 
3	5		conflicts slightly with
n/c	6		other data I gathered.
n/c	7
1,7	8 

I then went to my trusty box of serial cables (I am
a net admin and always keep around some spare cables)
and found 6 different brands of cables.  Here are
the pinouts;
			
			+-- WORKS!		+-- WORKS!
			|			|
			V			V

		Mac		Apple	Hayes	Business
		Ware	Unknown	540-05	07-	land
DIN8	Shiva	House	#1	56-A	00681	66688 
=======	=======	=======	=======	=======	=======	=======
1	20	6,20	4,20	20	4	20
2	5	5,8	5	6,8	5	6,8
3	2	2	2	2	2	2
4	1,7	1,7	7	7	1,7	7
5	3	3	3	3	3	3
6	n/c	n/c	n/c	n/c	n/c	n/c	
7	8	n/c	n/c	n/c	17	n/c
8	1,7	1,7	7	7	1,7	7

NOTE: The Hayes cable came with a bundle that included SmartCom
and a Hayes Ultra-96.

Luckily I didn't need to try each of these cables to 
find which worked and which didn't.  When I had dialed
into the Hayes BBS, I downloaded a utility that tests
cables between one of their modems and your modem port.

The only cables that worked were Unknown #1 and the Hayes
cable.  What do I do now to get more cables?  I dialed back
to the Hayes BBS and looked into their shopping forum.
It turns out that Hayes wants $32.95 for their percious
cable!!!  (Macwarehouse sells serial cables for $15.00).

Not knowing where the "Unknown" cable came from, I am now
searching for a cheap source of the correct cable.  Alternately,
I need a source for the Mini-Din-8 connector and I will 
make my own cables.  I contacted Black Box about a custom 
cable and their cost is about the same (list) but is $27 
with our corporate discount.  I am also in contact with 
Inmac.

I called several companies and found the following pinouts
(none of which will work according to my findings).

			Black
	Inmac	Misco	Box
DIN8	H074416	XD0265	TZEVMAI
=======	=======	=======	=======	
1	20	20	20
2	5,8	5,6,8	5
3	2	2	2
4	1,7	7	7
5	3	3	3
6	n/c	n/c	n/c
7	n/c	n/c	n/c
8	1,7	7	7

I find it totally CRAZY the differences in what the handshaking
in and handshaking out of the modem port is sometimes connected
to.  Take for example pin 2, this is the handshake into the 
Macintosh.  On several cables, this pin is connected to more
that one output from the modem (CTS and/or DSR and/or DCD). 
I was always taught that you should avoid tying output together.

Another example is the the MacWarehouse cable and what it does with
the Din-8 pin 1 (handshake out).  They tie this cpu output to 
both an output (DTR) AND AN INPUT (DSR) of the modem.  That means that
no matter what the CPU says to do, the modem will give itself
its own a handshake (maybe).  

Hayes (I think) has the right idea.  Handshake output to RTS
and handshake input to CTS.  Of course this ignores DCD totally
but Hayes must toggle CTS and DCD together internally.  As long
as the CPU gets a handshake input, all is well.

One thing that Hayes has the wrong idea on is not connecting DTR
to anything.  Most other brands of modems utilize DTR to determine
if the terminal is on line.  Thus the Unknown cable is a better
all around bet as it has more flexibility (maybe).

I submit that the ultimate cable has as many outputs of the modem
as possible go to the handshake input of the cpu.
Conversely, the handshake output of the cpu should go to as many
inputs of the modem as possible.  This would seem to work with as
many different styles of modems as possible and there would be 
no output to output bridges to fight each other.

Here is what I think is the ultimate Macintosh to Modem cable;

DIN8	Signal	DB-25	Signal(s)
=======	=======	=======	=========
1	HS out	20,4 	DTR,RTS
2	HS in	5,6,8	CTS,DSR,DCD
3	TxD-	2	TxD
4	Gnd	1,7	Gnd
5	RxD-	3	RxD
6	TxD+	n/c	
7	GPi	n/c
8	RxD+	1,7	Gnd


I will welcome any comments on this subject.  Please email them
to me and I will summarize.

Thanks for listening, John
-- 
=  Enjoy!          John DeRosa, Motorola, Inc, ESMR Development  =
=  thanks          derosa@ssd.comm.mot.com                       =
=  a 10^6          N1111@applelink.apple.com                     =

-- 
=  Enjoy!          John DeRosa, Motorola, Inc, ESMR Development  =
=  thanks          derosa@ssd.comm.mot.com                       =
=  a 10^6          N1111@applelink.apple.com                     =