Re: Nibble copy for other formats?

[Michael J. Mahon <mjmahon@aol.com>]

osgeld <kevin@hackaday.com> wrote:
> On Tuesday, March 12, 2013 7:18:40 PM UTC-5, schmidtd wrote:
>> On 3/12/2013 5:33 PM, osgeld wrote:
>> 
>>> On Tuesday, March 12, 2013 2:45:35 PM UTC-5, BLuRry wrote:
>> 
>>>> With parallel ports disappearing, [...]
>> 
>>> or a well behaved usb paralell port adapter
>> 
>> 
>> 
>> Not a viable solution with bit-banging operations (such as we're 
>> 
>> discussing here)
> 
> I dont see why not, its not quite as simple as a onboard legacy port, but
> they have all the same pins and capabilities, instead of direct bit
> banging you interface though the USB driver, otherwise those exact same
> pins driving your printer wouldn't drive your printer.
> 
> anyway just a thought

If the interface you wish to emulate is fully asynchronous (handshaking on
all state changes), then a USB-connected parallel port could be bit-banged,
though it might be too slow. 

If the emulated interface has synchronous state changes, then the inherent
non-determinism of the USB protocol--not to mention the non-determinism of
PC timing--would likely interfere with useful emulation. 

A simple example of such a synchronous interface is an Apple 5.25" floppy
drive. Nibble streams can only be read over USB if the actual nibble
capture is done by a micro controller (deterministic timing) and buffered
prior to sending over USB. The actual real-time drive handling cannot be
done over USB, any more than it could be controlled over a network. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon