Acorn IEEE488 interface
ard at p850ug1.demon.co.uk
Sun Dec 11 13:35:51 CST 2005
> I've also got the schematic for the Acorn System IEEE488 card somewhere - it
> wouldn't surprise me if the BBC unit is based heavily on this (I don't think I
It might be, it might not. The 'Acorn' IEEE-488 interface for the Beeb
doesn't seem to be an Acorn design.
The article to find is in 'Electronics and Wireless World' February 1984,
pages 24-26 ('IEEE488 interface for the BBC Microcomputer'). It imples
the interface was actually designed by a company called 'Intellegent
Anyway, there is a schematic. It's based round a 9914 chip along with the
75160 and 75162 buffers. There's a 5MHz clock circuit, an address
decoder, a data bus buffer, and the normal circuit to de-glitch the page
select line on the 1MHz bus. That's all. Nothing remotely odd.
Link S1 selects system controller mode, link S2 selects active pull-ups
on the IEEE488 data lines.
The other useful thing in this article is an example program using the
IEEEFS filesystem ROM, and a list of the commands you can use with the
interface. It appears you open a 'file' called "COMMAND" and another
called "DATA", you write command strings to the first one and use the
second one to actually transfer data on the bus. Addressing looks totally
strange, you seem to open a file with a name correspodning to the device
address in decimal and then use the file handle of _that_ file in
subsequent comamnds. Hmmm...
> I've also got a complete unit in the cupboard (but no BBC-side ROM to go with it)
> I *think* Tony Duell (on this list) has one too. Other than that, those are
I do. I think I might also have the IEEEFS ROM that goes with it, but I
can't promise that.
You;'ve just made me worried. I am going to have to try to find my unit
to see if it agrees with the circuit in Wireless World.
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