HP-IB, Amigo/cs80 was Re: hp 9153 floppy & disk

[Tony Duell]

> I've been tinkering with this idea for quite some time and have a couple of
> observations.
> 
> The project I'm been pondering would use AVR micro along with an IDE disk to
> emulate a CS80 drive. The IDE interface is pretty simple although like the
> HPIB it does requires a lot of I/O lines. Between all the handshaking and

IIRC, the interface to a CF card is essentially IDE, so you could use 
non-rotating memory if you wanted to.

> control signals with the IDE and HPIB devices, it would require a TON of
> I/O. Either that or you have to do some fancy muxing of the I/O.

Or you could use a microprocssor rather than a microcontroller with 
external ROM and RAM chips. Then hange the iDE drive off the bus as was 
origianlly intended, and connect up an HPIB controller chip or a parallel 
port chip to bang out the HPIB protocol. It puts the chip count right up, 
but it means the only programmed drvice is the firmware EPROM (which is 
easy to provgram)m and it's a lot easier to debug the firmware (you can 
use a logic analyser on the processor bus).

> 
> So, to make the HPIB control simpler, I'd prefer to use a HPIB controller
> chip like the NEC7210. That chip just hangs on an 8-bit bus and uses
> internal registers to free up some of the I/O lines on the micro. The
> biggest problem is finding a reliable supply of HPIB controller chips.

Yes, that's the problem. Most of the traditional HPIB interface chips 
have long beend discontinued. And ehile you might be able to fet them for 
repair purposed, I'd rahter not such a device in a new design.
 
> My solution to this would be to break this project in to two separate
> smaller projects. Firstly, use a separate microprocessor to emulate the 7210
> controller chip. This would provide several advantages:

Why do you need 2 mircoprocessors? The HPIB low-level protocol is simple 
enough that it could easily be handled by whatever chip is running the 
main software

> 3.) The 75160/1 pairs are still available. I think DIGIKEY has them in stock
> at a reasonable price. Note that these are not "just" I/O buffers. There are
> a few additional gates in the devices that add some more logic that one
> might expect.
> 
> So, the AVR could eliminate the need for the 75160/1 bus driver chips. If
> you fry a $4 AVR... Who cares? It doesn't cost much more than the dedicated
> drivers.

The problem is that the AVR needs to be programmed, It's a lot easier to 
replace a DIL packaged IC (particularly if you put it in a socket) than 
have to program a new AVR and plug it in.

I am also not sure (I would have to check) if the AVR (or any other 
mcirocontoller) poer pins meet the specs for driving/sensing an HPIB 
line. 

> 4.) You might be able to build a simple "adapter" board and use the AVR in
> place of hard-to-find 7210's in existing equipment.

I doubt it. I don't think an AVR on its own would be able to respond to 
the states of the host-interface address/data/control lines quickly 
enough. You'd need some hardware to provide the actually 'registers'. OK, 
it could be a CPLD or something, but this makes things ever more 
complicated. If you're goign to use CPLDs of FPGAs, you might as well 
make the entire HPIB interface in one and not use the AVR at all.

-tony