SCSI Controller Hanging...

Jack Harper harper at
Tue Jan 23 12:22:46 CST 2018

Great information/advice Jules.

I appreciate it - and know more about SCSI now than before.



At 11:15 AM 1/23/2018, Jules Richardson via cctalk wrote:
>On 01/23/2018 10:33 AM, Jack Harper via cctalk wrote:
>>Greetings to the List from the Snowy Rocky Mountains.
>>Beautiful clear sunny day here at +9F :)
>It's a toasty 20F here in northern MN :)
>>I have never before dealt with SCSI as a programmer - does this sound like
>>something is configured incorrectly?
>>There is not much to configure.
>I'm not sure about incorrect config, but I'm guessing it could be a 
>software issue (rather than hardware) - i.e. board reset is also 
>causing a reset of the SCSI bus in some odd way which is then 
>offlining/confusing any attached devices. Does it just happen with a 
>reset of one specific CPU board, or is it any of them?
>>I point out that I am not certain that I have the termination resistors
>Termination's easy enough - in theory :-)  A single set of 
>termination at each end of the bus, never in the middle - and 
>double-termination at either end will cause weird things to happen.
>If it's a 16-bit SCSI bus then you need termination either end of 
>both high/low 'halves' (sometimes people will park an 8-bit device 
>via a cable adapter at the end of a 16-bit bus, and stick an 8-bit 
>terminator on the device, which leaves the high side of the 16 bit 
>bus unterminated and causes glitches)
>*Something* on the bus needs to provide +5V on the SCSI TERMPWR 
>line; the terminators need this to work. I think typically the bus 
>adapter (i.e. controller) will do this, but I seem to recall that 
>the adapter in my Apple IIGS has no support for it and expects one 
>of the attached devices to do it (some will via a jumper setting, 
>but some won't)
>I think that some 16-bit devices will automagically work on an 8-bit 
>SCSI bus, but I don't know if there's any guarantee of that.
>Other than that, if you've got external devices then try and use the 
>best quality cables that you can find - there used to be some really 
>cheap junk out there which could cause all sorts of oddball problems.

Jack Harper, President
Secure Outcomes Inc
2942 Evergreen Parkway, Suite 300
Evergreen, Colorado 80439 USA

303.670.3750 (fax) for Product Info. 

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