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Retro Replay emulation in the 1541U2
http://retrohackers.com/viewtopic.php?f=20&t=626
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Author:  Frantic [ Fri Jul 22, 2011 6:04 pm ]
Post subject:  Retro Replay emulation in the 1541U2

Hello!

I recently got into RR hacking and like several others on here I am making my own custom ROM. I now have some questions regarding the Retro Replay emulation in the 1541U2:

The "Inside_Replay_Essentials.txt" states:

"any clone hardware emulating AR and RR hardware "seperately" in some
way should by default enable any accessory connector and of course the
REU compatible memory map. Clone devices such as the 1541u may choose to "ignore"
$de01 write accesses rendering it to a non-register effectively.
'''We hereby swear we will not use $de01 for setting or reading back the current ROM bank!'''
"

...but what if I develop a ROM that should actually have the accessory connector disabled? I rather want to have a MIDI interface connected at the same time as the cart, using a cart port expander, and the MIDI interface uses $de04 to $de07, so I don't want stuff like SilverSurfer/RR-Net to appear at those adresses.

1. Is the 1541U ignoring the accessory connector enable bit and just assuming that it is always enabled, as stated in the "Inside_Replay_Essentials.txt" or does it care about writes to $de01 after all?

2. In any case, do you know if there are any reasons to believe that it should be impossible or possible to use a MIDI interface at $de04-$de07 at the same time as a RR ROM (in both real RR hardware and the 1541U2 RR emulation)?

3. What is it that actually happens when the accessory enable bit is turned on and off respectively? Of course disabling it will make the RR-net/SilverSurfer go away, but... What if it is enabled and some other hardware (but not RR-Net/SilverSurfer) is available at $de04 for example (such as a MIDI interface at the same time as the RR cart using a cart port expander)? Does the accessory enable bit on the RR matter for other hardware like that? I mean.. is the RR "sniffing" the signals otherwise going to $de04 or something like that? (yes, my understanding of the hardware processes involved are quite fuzzy).

If you can help me out, I would be most happy. Question 1 and 3 are the most important questions here for me. Thanks!

//FTC

Author:  RaveGuru [ Mon Jul 25, 2011 4:51 pm ]
Post subject:  Re: Retro Replay emulation in the 1541U2

I've never used a port expander and I don't think there is any logic on *Replay hardware that "cuts" the address bus signals. But if the expansion port design is such that by default, lines are pulled low or high by expansion hardware, there might be a problem using multiple expansions/cartridges concurrently. But I guess that's what port expanders allow you to do, right? It's not much of a theory and I'm not a hardware guy but if the assumption is correct, then it should work! :)

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