Date   : Mon, 12 Jan 2004 18:30:57 +0000
From   : Richard Gellman <splodge@...>
Subject: Re: Host adapter Issue D

The host adapter board by default is self-terminating, i.e. fitted with 
terminating resistors on the 1Mhz bus where necessary. In order to add a 
second, you will need to not only fiddle its memory-mapped address using 
the bodge-o-matic link, but also remove the terminating resistors from 
the 1Mhz bus side.

The device chain for the 1Mhz works like SCSI, that is the last device 
on the chain needs the termination, so your chain would be:

BBC Micro
v
First host-adapter, non-terminated (resistors removed)
v
Second host-adapter, terminated (resistors intact).

Note that the only resistors to touch are on the 1Mhz bus side, the 
terminating resistors on the SCSI side MUST remain in place on BOTH boards.



Mark Usher wrote:

>Philip Blundell wrote:
>  
>
>>My issue D board does not have that change.  It sounds like this
>>modification is probably altering the address that the board will
>>respond at on the bus.  The '138 is a 3-to-8 line decoder; 
>>pin 15 is the Y0 output, and pin 13 is the Y2 output.
>>    
>>
>
>Pete Turnbull wrote:
>  
>
>>That changes the interface addresses from FC40-FC43 to FC48-FC4C.
>>Maybe that's why it's not responsive!  Perhaps someone modified this
>>to work in a multiple-adaptor system.
>>    
>>
>
>And as if by magic the hard drive appeared. Thanks for that. Now to do
>some tests to see if this board will work well straight through to SCSI
>drives. I think also I *must* hook up 2 host adapters to one system for
>the fun of it.
>
>To put both on the 1MHZ bus must I simply put them on the same 34 ribbon
>cable?
>
><BBC>-------->Host 1<------->Host 2<
>
>Or is some sort of termination recquired?
>
>
>-Mark
>
>
>  
>