SCSI Controller Hanging...

[Jack Harper]

Great information/advice Jules.

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

Regards,

Jack



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
>>correct.
>
>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.
>
>cheers
>
>Jules
>
>

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Jack Harper, President
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