Date   : Sun, 12 Aug 2007 13:55:42 +0200 (BST)
From   : johan@... (Johan Heuseveldt)
Subject: Emulating Econet hardware?

Hi,

On Sun 12 Aug, Jonathan Graham Harston wrote:
> Johan Heuseveldt <johan@...> wrote:

> > > Econet uses a 16-bit 'address' - net.stn - but as to the ALDC,
> > > everything after the opening flag is just 'data', it's irrelevant
> > > what that data is.
> > 
> > No, it isn't.
> > The first byte is the Address field for the 68B54. The first NMI handler
> > set up is expecting that, and tests for it.
>  
> Yes, the handler, ie, the software, not the hardware.

But you said (see above:)

  but as to the ALDC, everything after the opening flag is just 'data'
      ^^^^^^^^^^^^^^

which is not exactly true! ;-)

[...]

> > Normally the data is received per two bytes - CtrlReg 2, bit1, and
> > interrupts are prioritized - CtrlReg 2, bit0. The Address field has a
> > higher priority than normal data, so this very first byte - after the
> > opening flag - causes an Address field interrupt.
>  
> Otherwise known as 'Frame Start interrupt'.

OK, nothing against that! :-)

> > Also note that the Address field is an ADLC 68B54 property, and has
>  
> It's a Data-Link Control property,

Sorry, of course you're right.
I meant the 6854 reacts on this first byte specificly.

[...]

> which the 6854 and the Z80SIO
> implement. With the 6854 the software has to implement that property
> imbued in the first byte of the frame, and set 'ignore this frame'; with
> the Z80SIO it can implement that property itself setting the 'ignore this
> frame' by itself. The 'first received character' interupt then occurs on
> the second byte in the frame. The Econet software handler then checks that
> byte as the network number, setting 'ignore this frame' if it not &00 (my
> net) or &FF (broadcast).

Rejection is completely by hardware; definitely an advantage.
But, yes, acceptance still needs software to test the network part.


> There's a good quote in the Z80SIO datasheet: "Although the Z80-SIO
> device at first appears to be bewilderingly comples..." :)

It took me a day (yesterday), but at last - in the late evening - I
succeeded in the download of the Z80-SIO Technical Manual. It's a bit
pitty though that the quality (on screen) isn't too good. In particular
in the SDLC section, some part of the text is almost white.
Earlier, the down load of a more general descriptive document was ok.

Yes, I see both are xDLC's, and therefore similar.

I didn't know exactly how the 6854 conforms to the world standards,
and how much was proprietary of Motorola. Though the datasheets are
clear in mentioning HDLC and SDLC as standards, together with the
procedures (ADCCP), I didn't know how to interpret it. Now, having
read about the Z80-SIO, I realised both are for standards already
there.
(and more things are realised now about Econet)


Johan,

-- 
Johan Heuseveldt <johan@...              >
  aka  waarland

  The best place is a Riscy place
 
"Cap'n, I dinna know how much longer the engines will
hold out under the stress o' warp factor nine!"