Date   : Mon, 03 May 2004 23:09:22 +0100
From   : "Christopher Thornley" <c.j.thornley@...>
Subject: Re: B+ Upgrades

 Hi,
DRAMS hmm that kind of complicates things.
The photograph of the board shown on here has
2 x HB81464-12 (64KB x 4) === Very hard to find.
1 x SN74ALS10N === TriInput NAND
1 x 74LS158N   === QUAD 2-Input Multiplexer (8 to 4) 
                        Basically a 4 pole 2 Position Switch
                        (Obsolete) 
A host of other components some how linked together.

According to the Bplus64Fitting Instructions the following pin connections
are made.
QA
C/D
4M
ENB
RSL
2M
ENCAS
PGRAM
0/1

And a track cut.

The pins descriptions above mean nothing to me as I don't know what's
provided by them or how they interlink.

The connector below I assume 
RD0 to RD07 are data I/O lines
XA0 to XA7     are some type of address lines which can only access 2^8
256 bytes
nCAS and nRAS must be the column and row refresh etc of DRAMS
nDW Not to sure about that one ???

Not to sure if any of these will be suitable equivalents if I can track any
down http://www.amiga-stuff.com/hardware/64kx4-dram.html 

I have also found this which might help me
http://www.sxlist.com/techref/mem/dram/olmstead.html

I'll have a look but I don't think I'll be able to come up with a usable
circuit which will work in a similar way to the old one.

Any advise

Thanks
Chris



               />      Christopher J. Thornley is cjt@...
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-----Original Message-----
From: Majordomo List Manager [mailto:majordomo@...] On Behalf Of
John Kenyon
Sent: 03 May 2004 22:27
To: 'bbc'
Subject: RE: [BBC-Micro] B+ Upgrades

My (tattered) B+ circuit diagram doesn't show any provision for the extra
64k however it does show a 32 pin connector with the legend
"IC96 TM4164EK8-12 (Option to replace 8 off 4164-12)"
It looks to me, that using a couple of 62256 32kX8 SRAMs wouldn't be
possible using this connector - only DRAM would do.

The pins are marked/connected as follows:
1      OV
2      +5V
3&4        RD0     (i.e. DI and DO tied together on the PCB)
5      nCAS
6      XA7
7      XA5
8      XA4
9&10       RD1
11     nDW 
12     XA1
13     XA3
14     XA6
15&16      RD2
17     XA2
18     XA0
19     nRAS    
20&21      RD3
22     Ov
23&24      RD4
25&26      RD5     
27&28      RD6
29&30      RD7
31     0v
32     Not Connected

Hope this helps.

/John


> -----Original Message-----
> From: Majordomo List Manager [mailto:majordomo@...]On Behalf 
> Of Christopher Thornley
> Sent: 02 May 2004 23:02
> To: 'gARetH baBB'; 'bbc'
> Subject: RE: [BBC-Micro] B+ Upgrades
> Importance: High
> 
> 
>  Hi,
> Please could you send me a picture of the track side of the board.
> I has acquired a BBC+ 64k machine and would like to upgrade it to 64k 
> swr RAM but these interface or chip are not available any more.
> I would like to build an equivalent unit but I need to you the 
> original circuit diagram and which pins on the connector it was connected
to.
>