Mega ST's bus

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Mega ST's bus

Postby mikro » Mon Feb 06, 2017 10:24 am

I've been reading some docs and I've realised that I've never seen any mention of the Mega Bus address range. For VME it's pretty well defined on both the MegaSTE and TT but the Mega ST... no trace.

And while we are at it, is Mega ST's RTC unique for the machine itself? I mean, MegaSTE/TT/Falcon's RTC is somewhere else but maybe the address of MegaST's RTC was used in some hardware mods, too?

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Re: Mega ST's bus

Postby jvas » Mon Feb 06, 2017 11:26 am


mikro
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Re: Mega ST's bus

Postby mikro » Mon Feb 06, 2017 10:34 pm

Hmm, so

C00000 ~ CFFFFF
FF0000 ~ FF7FFF
FFFE00 ~ FFFFFD
FFFFFE ~ FFFFFF

Nice. Do you know what happens if one tries to read from such location and nothing is in the mega slot?

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Re: Mega ST's bus

Postby Arne » Tue Feb 07, 2017 5:12 am

mikro wrote:Hmm, so

C00000 ~ CFFFFF
FF0000 ~ FF7FFF
FFFE00 ~ FFFFFD
FFFFFE ~ FFFFFF

You can combine the last two ranges to:
FFFE00 - FFFFFF

mikro wrote:Nice. Do you know what happens if one tries to read from such location and nothing is in the mega slot?

As usual: Glue will assert /BERR: two bombs.
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Re: Mega ST's bus

Postby DarkLord » Tue Feb 07, 2017 12:02 pm

Not sure about this, maybe someone can verify.... Are the STacy's and
Mega ST's RTC's similar?

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Re: Mega ST's bus

Postby joska » Tue Feb 07, 2017 12:45 pm

mikro wrote:I've been reading some docs and I've realised that I've never seen any mention of the Mega Bus address range.


The MegaBus is just the 68000 signals. So it has the same address range as the 68000. Any cards that connects to the MegaBus will have to do their own address decoding.

mikro wrote:And while we are at it, is Mega ST's RTC unique for the machine itself?


The Mega ST use a Ricoh RP5C15 RTC, which IIRC is the same as in the Stacy and Mega STE.
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Re: Mega ST's bus

Postby mikro » Tue Feb 07, 2017 10:06 pm

joska wrote:The Mega ST use a Ricoh RP5C15 RTC, which IIRC is the same as in the Stacy and Mega STE.

But the MegaSTE (not sure about Stacy) uses a completely different address space (and registers) to read/write time, AFAIK the chips are not the same.

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Re: Mega ST's bus

Postby joska » Wed Feb 08, 2017 6:16 am

According to the schematics the MSTE use the same RS5C15 RTC as the Mega and Stacy. I don't remember the register addresses on the Mega - maybe they have been changed in the MSTE because the Mega addresses are in the VME address range?

Edit: Just had a look at https://mikro.naprvyraz.sk/docs/Memory%20Maps/HARDWARE.TXT. The addresses for the realtime clock is well above VME address range. Also, I could not see any MSTE specific rtc-registers here. Are you sure you are not thinking about the TT rtc?

mste-rtc.png
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