Newsgroup: it.comp.hardware.scsi
Titolo: SCSI 25-pin DIN connector pinout.

Hi,
	I have an Umax Astra 1220S SCSI scanner. This comes with an ISA SCSI card that
fits in the PC. Both the SCSI card and the scanner use a 25-pin DIN connector. 
I'd like to move the scanner from the PC and put it on my Sun Ultra 60 Unix
workstation. The Sun has a 68-pin SCSI connector, so I bought a 68-25 pin SCSI
cable from B & A computer via eBay.
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=2000147708
The Sun workstation is used with an external disk which auto-terminations. The
disk enclosure also has LEDs to indicate the termination - whether the low byte,
high byte, neither or both are termination. Despite the scanner being at the end
of the SCSI chain, the disk does not detect it, so terminates the scsi bus at
the disk - see below.
Sun workstation===Disk1===Disk2---Scanner---terminator.
==== is 68-pin wide scsi
---- is SCSI down a 25-pin DIN lead.
The terminator (25-pin DIN) is fitted on the directly back of the scanner.
I would expect 'Disk2' to terminate the high bytes, but leave the low-bytes
unterminated, since the scanner's terminator does that. However, 'Disk2' seems
unaware of the scanner's presence. 
Is there a standard for how the 25-pin SCSI DIN connectors are wired? I'd like
to check if the cable is wired okay. Normally SCSI cables are 50 or 68-pins, so
I'm wondering if this is wired okay. 
Are there any other problems I'm likely to come across in fitting a narrow
scanner on a 25-pin lead to a wide (68-pin) SCSI bus? I am concerned it might
impact the performance of my SCSI bus, so have ordered another SCSI controller
to fit in the Sun. For now however, I don't have that luxury. 
-- 
Dr. David Kirkby PhD,
email: 
drki...@ntlworld.com
 
web page: 
http://www.david-kirkby.co.uk/
Amateur radio callsign: G8WRB

 wrote in message news:3C6EE6BA...@ntlworld.com...


 solution.
I did notice a warning when the system booted about dropping the speed of the
SCSI bus, so I think performance would be compromised, as one of my 10,000 rpm
Cheetah hard drives is on this controller. It rather defeats the object of a
fast hard drive if the bus gets slowed down!
I'll see what happens once I get a new dual SCSI card and will be able to move
put the scanner on that. In order to use my present cables I will still have to
add a Sun 611 enclosure to ensure termination, but at least there will be only
one - not 2 external disks and a tape drive. Perhaps there is too much on the
bus. 
Dr. David Kirkby.


 wrote in message news:3C6F8334...@ntlworld.com...
} Michael wrote:
} > 
} > Most 68-25 pin cables (including the one you got on eBay) do not
} > provide high byte termination, and there's no way the disk enclosure
} > would know to terminate it either.
} 
} I would beg to differ there. The disk enclosure, a Sun 611 box, is capable of
} working out if something is terminated or not. The rear clearly states "auto
} termination". If you put nothing on the 68-pin output connector, then the two
} leds light up to indicate it is terminating both the low and high bytes. If
} instead another 68-pin device is put there, both LEDs extinguish, indicating the
} disk enclosure is not terminating. 
} 
} If I've put 50 pin devices on its output, like a CD-ROM, so the enclosure only
} terminates the high bytes, with one LED lit (high byte) and the other
} extinguished (low  byte). I did this with no problem on my external CD-writer,
} and never had a problem with it. It is quite neat really and one of the good
} points about the CD
} 
} However, with the scanner's 25-pin connector, this does not happen, which is
} making me think the cable might be wrong. Perhaps the enclosure determines what
} is connected by using a line which is not connected in my cable? 
If that's the case then the problem is likely the scanner terminator.
Are you using the one Umax shipped with the 1220S?  It's passive,
replacing it with a 25 pin active terminator may help.
Mike

 Mike
That's an interesting thought - I am indeed using the scanner's terminator. I've
no idea if its active or not, but there is no LED as I've seen on some active
ones. Its possible the Sun's active terminators don't sense the presence of this
terminator, so they don't terminate the low bytes as they should. 
I've never seen active terminators in 25-pin DIN, bit I've never really looked
for them either. The new SCSI card (its a dual one) should arrive next week, so
if that does not improve things, I will try to find a 25-pin active terminator. 
This Sun will soon have 4 separate SCSI buses - two separate buses on the PCI
card, an internal SCSI bus and an external one. Hopefully with 4 buses I can
move things around and some way find a combination that works. 


 wrote in message news:a4mug3$1ecmc$1...@ID-82690.news.dfncis.de...
: Most 68-25 pin cables (including the one you got on eBay) do not
: provide high byte termination, 
: and there's no way the disk enclosure would know to terminate it either.
Apparently it does by sensing the out connector.
What I find interesting is that it differentiates between low and highbyte.
: 
: What you need is a 68-to-50 pin adapter at the enclosure, one that

: 

 wrote in message news:3C6FA481...@ntlworld.com...
} Michael wrote:
} 
} > If that's the case then the problem is likely the scanner terminator.
} > Are you using the one Umax shipped with the 1220S?  It's passive,
} > replacing it with a 25 pin active terminator may help.
} > 
} > Mike
} That's an interesting thought - I am indeed using the scanner's terminator. I've
} no idea if its active or not, but there is no LED as I've seen on some active
} ones. Its possible the Sun's active terminators don't sense the presence of this
} terminator, so they don't terminate the low bytes as they should. 
Umax's 25 pin terminators are definitely passive.
} I've never seen active terminators in 25-pin DIN, bit I've never really looked
} for them either. The new SCSI card (its a dual one) should arrive next week, so
} if that does not improve things, I will try to find a 25-pin active terminator. 
They're not easy to find.  Belkin sells them, do a web search
for their part# which is "F2N959-B".
} This Sun will soon have 4 separate SCSI buses - two separate buses on the PCI
} card, an internal SCSI bus and an external one. Hopefully with 4 buses I can
} move things around and some way find a combination that works. 
Good luck,
Mike

 wrote in message news:3C6FA481...@ntlworld.com...
: Michael wrote:
: 
: > If that's the case then the problem is likely the scanner terminator.
: > Are you using the one Umax shipped with the 1220S?  It's passive,
: > replacing it with a 25 pin active terminator may help.
: > 
: > Mike
:
: That's an interesting thought - I am indeed using the scanner's terminator. I've
: no idea if its active or not, but there is no LED as I've seen on some active
: ones. Its possible the Sun's active terminators don't sense the presence of this
: terminator, so they don't terminate the low bytes as they should. 
: 
: I've never seen active terminators in 25-pin DIN, bit I've never really looked
: for them either. The new SCSI card (its a dual one) should arrive next week, so
: if that does not improve things, I will try to find a 25-pin active terminator. 
: 
: This Sun will soon have 4 separate SCSI buses - two separate buses on the PCI
: card, an internal SCSI bus and an external one. 
Hopefully you don't confuse connectors with buses like that second part of that 
sentence seems to imply.
: Hopefully with 4 buses I can move things around and some way find a combination 


 wrote in message news:3C6F8334...@ntlworld.com...
: Michael wrote:
: > 
: > Most 68-25 pin cables (including the one you got on eBay) do not
: > provide high byte termination, and there's no way the disk enclosure
: > would know to terminate it either.
: 
: I would beg to differ there. The disk enclosure, a Sun 611 box, is capable of
: working out if something is terminated or not. The rear clearly states "auto
: termination". If you put nothing on the 68-pin output connector, then the two
: leds light up to indicate it is terminating both the low and high bytes. If
: instead another 68-pin device is put there, both LEDs extinguish, indicating the
: disk enclosure is not terminating. 
: 
: If I've put 50 pin devices on its output, like a CD-ROM, so the enclosure only
: terminates the high bytes, with one LED lit (high byte) and the other
: extinguished (low  byte). I did this with no problem on my external CD-writer,
: and never had a problem with it. It is quite neat really and one of the good
: points about the CD
Would this be a special make, specifically for SUN or is the cable a SUN 
approved one?
: 
: However, with the scanner's 25-pin connector, this does not happen, which is
: making me think the cable might be wrong. Perhaps the enclosure determines what
: is connected by using a line which is not connected in my cable? 
Well, unless there is some specific arrangement using two sense lines that disting-
uish between a narrow and wide conductor arrangement I would guess a single con-
nector sense line to enable/disable sensing and two narrow terminator chips with 
auto sensing capability like some chips from DALLAS can. If that sense line is not 
wired in the cable, the box's terminators will act like there is no cable attached.
:  
: > What you need is a 68-to-50 pin adapter at the enclosure, one that
: > does provide high byte termination, then use a 50-to-25 pin cable
: > to the scanner.
: 
: I'm sceptical this is necessary, for the reasons stated above. It is also a
: nuisance, since the cable I have is 25<=>68, not 25<=>50. 
:  
: > 25 pin SCSI is an Apple kludge which is often problematic.  Your
: > decision to install the scanner on a separate card is really the best
: > solution.
: 
: I did notice a warning when the system booted about dropping the speed of the
: SCSI bus, 
Unless it is an LVD SCSI bus, it shouldn't.
: so I think performance would be compromised, as one of my 10,000 rpm
: Cheetah hard drives is on this controller. It rather defeats the object of a
: fast hard drive if the bus gets slowed down!
Not necessarily with a single harddrive or harddrives in single tasking use.
: 
: I'll see what happens once I get a new dual SCSI card and will be able to move
: put the scanner on that. In order to use my present cables I will still have to
: add a Sun 611 enclosure to ensure termination, 
Not necessarily if the controller allows you to set termination for High and Low 
byte.
: but at least there will be only


 sentence seems to imply.
No I'm not confusing connectors and buses. 
The SCSI controller in my Sun Ultra 60 workstation is a dual one. One bus is
used internally for the two disks and CD, with a second bus available on a
68-pin connector externally. They are separate, so there is no problem in having
two devices on the same SCSI id, as long as one device is inside the case and
the other outside. 
I've bought a Sun SCSI card, that has 6 connectors in total, but on two buses.
I'm hoping that by moving my scanner to its own bus I might be able to get it
working properly. I've not got the card yet, so can't say for sure if that will
improve matters. 


 wrote in message
: > news:3C6FA481...@ntlworld.com...
:
: > : This Sun will soon have 4 separate SCSI buses - two separate buses on the PCI
: > : card, an internal SCSI bus and an external one.
:
: > Hopefully you don't confuse connectors with buses like that second part of that
: > sentence seems to imply.
:
: This sentence seems to imply that you are confused about the Sun Ultra 60.
Nope, not confused, just unfamiliar.
Not many boxes have seperate channels dedicated to sole external and sole internal use.
It takes away some of the practicality that way that dual channel otherwise offers.
: The Sun Ultra 60 has two SCSI buses on the mainboard, one is used for
: internal devices and one is for external devices.
:
: --
: Göran Larsson     hoh AT approve DOT se