Re: IEEE488 electrical specs
Date: 2001-04-18 21:53:33

Hallo Martijn.
> > I have to dig up the exact info at home. But AFAIK you should recon with
> > about 3 Kohm for every line. 
> .                        ^^^^^
> Shouldn't that read 'device' ?

No, line, or better: pin. 

The specs of TI's SN75160B and SN75161B say a 1.7 K resistor plus a diode 
for every output pin. Less then I thought :( 
(5 - 0.6) / 1700 = 2.6 mA. So 6 devices shouldn't be a problem.

> Programming a 8751 isn't really difficult. I have the specifications 
> floating somewhere on my desk at Philips. Interested in a copy? 

Unfortunally it seems I don't have a 8751 although I still believe I have 
at least one (but where ???). 
On the other hand I found some 8741's, 8742's, 8748's and 8749's. I have 
the Philips databook IC14 which contains info about the 8048 and 8049. But 
NOT how to program them. I also have some 8048's but have no idea how to 
find out if they are programmed or not.
AFAIK I don't have anything about the 8741 and 8742. If you have any info 
on these, I would be glad if you could help me with the specs of these, 
I know the ML for these and the 8x51 differ but that shouldn't be a problem 
if you would be so kind to donate the sources.

Looking for the 8751 I bumped in something else from the time I worked at 
NatLab: two 8051 PODs, a V85C552 and a V85C582. Interested?

I also found a loose 80552 which reminded me I have an Elektuur-card 
equiped with this controller. IMHO this one could be used as well. I only 
hope I have enough I/O-pins left for the interface self is this card is 
equiped with an EPROM and SRAM.

> It would be a shame if the connection between the PET and the 4040 would 
> be slowed down because of the 1541..

You would loose some time in the initial phase where all devices have to 
check if the given devicenumber is theirs. It shouldn't slow down the 
actual data transfers.

> Hmm. I don't really follow you here. A 8751 has 4 I/O ports

At that moment I thought 3. No databooks at hand to verify.

> (It may be possible to reclaim a few IO lines though, 
> I don't think that you'll need the full address range of 64K)

For IEEE you need 8 datalines and 6 controllines (REN and SQR not needed), 
for IEC only three: DATA, CLK and ATN. RESET is covered by IFC. That makes 
17. Two for simple RS232 makes 19. Five left which enables you 8K of EPROM. 
Which is a lot, I thought. 

> Regarding an extra RS232 port: The 8751 has a built-in RS232 port; if
> you want to add a *second* one, you'll end up bit-banging such a thing.

I meant the build-in one indeed.

> Maybe not; maybe I can abuse the UART for that..

Very smart indeed, petje af :) 
But if RS232 is possible, why not. I programmed more then just a little bit 
8051 ten years ago. (the above Elektuur 80552 I used for an electronic 
ignition for a VW Beetle with on-the-fly tuning while driving it on a 
testbank) If I remembered well, the RS232 communication, once started, 
didn't need any further attention. This enables us to check the IEC/IEEE 
bus for further transfers. 

Groetjes, Ruud

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