Date   : Mon, 03 May 2010 12:13:36 +1030
From   : station240@... (paul aslin)
Subject: 68B54 memory locations and ANFS puzzle

> From: robert@...
> Date: Fri, 30 Apr 2010 13:39:09 +0100
> To: bbc-micro@...
> Subject: Re: [BBC-Micro] 68B54 memory locations and ANFS puzzle
>
> On 30 April 2010 13:10, paul aslin  wrote:
>> Referring to the memory map at:
>> http://mdfs.net/Docs/Comp/BBC/AllMem
>>
>> It shows the B/B+ to have the 68B54 in one memory location, and a different
location in the Master.
>> &FEA0-&FEBF 6854 ADLC Econet controller (B/B+)
>> &FEC0-&FEDF 6854 ADLC Econet controller (Master)
>>
>> But decompiling ANFS 4.25 shows it only uses &FEA0 to &FEA3
>
> I've never got into poking about in the hardware on a real Master, but
> when I initially added Econet support to BeebEm I just specified
> FEA0-BF for all computer types - just checked the 4.11 source and
> it's still the same, and it seems to work fine ...
>
> It does seem wasteful to give it 32 possible addresses for just 4
> registers, but it simplified the address decoding. Similarly the
> address jumpers/NMI toggle at FE18-FE1F (on the B) get 8 addresses,
> when they only need one.
>
> Rob

Actually even the 16 possible addresses aren't fully accessible to existing
econet/ethernet cards as none physically plug into A2 and A3. Hence are limited
to 4 addresses.

With a bit of extra hardware its possible to use the remaining 12 addresses
for an internal upgrade, say a hard drive controller.
                                         
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