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ECB-VGA3 Running [message #6768]

Wed, 13 November 2019 18:53

rcini
Messages: 64
Registered: October 2015
Location: Long Island, NY

Member

All --

Just a quick note to let everyone know that I successfully built the (relatively uncommon) VGA3 board for use with BIOS045 and the SBC-188 board. It's a 4-layer board, so extra care with soldering is needed especially on the power pins. There were no problems with the assembly, other than the picture on the Wiki is taken at an angle, so it's hard to tell which pins the jumpers go on (I used the picture rather than the schematic).

Redraw speed is pretty good but you occasionally see redraw artifacts. Overall, an excellent board.

Rich

Rich Cini

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Re: ECB-VGA3 Running [message #6771 is a reply to message #6768]

Thu, 14 November 2019 06:46

jcoffman
Messages: 332
Registered: October 2015

Senior Member

Rich,

Glad to hear you have the VGA3 running with your SBC-188. This is the only RetroBrew CPU board that uses the direct addressing of character memory. Scrolling is arduous, as all of the displayed memory has to be moved, and the fleeting artifacts are a consequence.

The UNA and RomWBW implementations do not use direct memory writes, but use the slower I/O write mechanism; however, they both scroll by altering the refresh regeneration pointers in the CRTC. Scrolling is faster and avoids the artifacts. Same could be done on the SBC-188, but then IBM-PC compatibility would be lost: a lot of programs want to write to character memory on their own.

I think you'll find monochrome mode 7 works just as well as color mode 3.

--John

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Re: ECB-VGA3 Running [message #6779 is a reply to message #6771]

Sat, 16 November 2019 02:20

b1ackmai1er
Messages: 396
Registered: November 2017

Senior Member

Hi Rich,

I'm stuck on the 47K bussed array resistors. Do you have any spare you would care to part with (two required)? Have some 9-pin units on order and was going to run a single resistor to the last pin but it would be nice to finish this off pretty-like.

Regards Phil.

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Re: ECB-VGA3 Running [message #6781 is a reply to message #6779]

Sat, 16 November 2019 05:14

rcini
Messages: 64
Registered: October 2015
Location: Long Island, NY

Member

Phil --

The BOM shows 3 are required. I happen to have 3 left. Jameco part# 1180365. PM me and I will drop them into the mail on Monday.

Rich Cini

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Re: ECB-VGA3 Running [message #6784 is a reply to message #6779]

Sat, 16 November 2019 07:54

jcoffman
Messages: 332
Registered: October 2015

Senior Member

Phil,

In electrical engineering, it is amazing what you can get away with. The 47K resistor packs (3 places) are specified to limit power consumption. There is no problem using 33K, 22K, 15K, or 10K. FYI: the Q- inputs on the '682's have 20K (approx. Wink

pull-ups. The only difference you would see would be power consumption. I would not suggest going below 10K, although it would work fine.

--John

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Re: ECB-VGA3 Running [message #7600 is a reply to message #6768]

Mon, 04 May 2020 05:23

trick-1
Messages: 164
Registered: September 2016

Senior Member

You can always use discrete resistors and run a bar across the top...doesn't look the best but it can get a board finished. I also find I end up with lots of SIP resistor packs and they are never the right size.....

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Re: ECB-VGA3 Running [message #7601 is a reply to message #7600]

Mon, 04 May 2020 06:12

jcoffman
Messages: 332
Registered: October 2015

Senior Member

RE: SIP resistors

I have found that you can take a pair of diagonal cutters and trim a 10-pin SIP down to a 5-pin size. 98% of the time, when you check the resulting "shortie" with an ohmmeter, it is fine.

--John

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