600D Colour RAM. Help!!!! SOLVED!

waltermixxx
Posts: 118
Joined: Sun Feb 03, 2019 10:31 pm

Re: 600D Colour RAM. Help!!!!

Post by waltermixxx » Sun Jun 09, 2019 4:37 pm

Woot Woot, just like Sesame Street always taught me,
cooperation is key. :)

Cheers, it was a fun night of OSI goodness, pizza and a very strange movie....

:)
Turning into quite an OSI Junkie (HTFDTH?) Superboard II REV B-40K, 9600b, HC-05 Bluetooth, Superboard II Rev D, C4P rebuild- 502, 542c, 540B. :)

dave
Site Admin
Posts: 560
Joined: Tue Sep 09, 2008 5:24 am

Re: 600D Colour RAM. Help!!!! SOLVED!

Post by dave » Tue Jun 11, 2019 7:03 pm

Interesting. A write or read to D000-D7FF will cause the appropriate 2114 chips (character or color) to be selected. But U56 determines when the CPU address lines are used to address the RAM, and when the video counters are used. So with /A10 jumpered to U56, the CPU address lines are routed to the video RAM chips when the CPU tries to read or write D000-D3FF. But whatever random address is on the video counter chain will be applied to the address lines for a CPU read or write to D400-D7FF. So the read and writes to the video RAM should appear randomly ordered in RAM.

Jumpering the pin high routes the CPU address lines to the RAM chips for all addresses D000-D7FF.

Dave

Steve Gray
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Joined: Mon Oct 06, 2008 1:54 pm
Location: Markham, Ontario, Canada
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Re: 600D Colour RAM. Help!!!! SOLVED!

Post by Steve Gray » Tue Jun 11, 2019 8:30 pm

dave wrote:
Tue Jun 11, 2019 7:03 pm
Interesting. A write or read to D000-D7FF will cause the appropriate 2114 chips (character or color) to be selected. But U56 determines when the CPU address lines are used to address the RAM, and when the video counters are used. So with /A10 jumpered to U56, the CPU address lines are routed to the video RAM chips when the CPU tries to read or write D000-D3FF. But whatever random address is on the video counter chain will be applied to the address lines for a CPU read or write to D400-D7FF. So the read and writes to the video RAM should appear randomly ordered in RAM.

Jumpering the pin high routes the CPU address lines to the RAM chips for all addresses D000-D7FF.

Dave
And you wonder why this wouldn't be the default, unless they just didn't want to interfere with some other possible use of the colour memory space.

Steve
C4P working, C1P working. 600D Replica working, C4P+D&N floppy not working. 505 board, 610 board, Mittendorf board, TOSIE hacker board need testing, PicoDOS disk untested.

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