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uPD7220 vs uPD72020 [message #9852]

Wed, 06 April 2022 04:01

lynchaj
Messages: 1080
Registered: June 2016

Senior Member

Hi
The Z180GDC V1 board seems to be working well enough and now am contemplating some modifications for improved performance.

First item is replacing the uPD7220 (NMOS) with uPD72020 (CMOS). Originally I was hoping to do this purely for reduced power usage but it also appears there are some beneficial software improvements as well. Does anyone have experience in replacing the uPD7220 with uPD72020 and/or programming it? They appear to be pin compatible and software compatible but the uPD72020 is more recent and has some improvements.

Second possibility is DMA which the NEC uPD7220 user manual documents but unfortunately only for the Intel 8237. I think the concepts would be similar for Z180 but it will take some research and experimentation to get the right design. Has anyone tried this before and how did it work out?

Third is uPD7220 as a shared memory architecture similar to the MC6845. Has anyone seen or worked with anything like this? Allowing the CPU direct access to the video memory would enable a lot of functionality and improved performance but at a significant cost in complexity. Also the video RAM is 16 bits wide versus the Z180 which is only 8 bits wide. It might make better sense with a true 16 bit wide CPU like 8086 or 68000.

Thanks, Andrew Lynch

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Re: uPD7220 vs uPD72020 [message #9856 is a reply to message #9852]

Sat, 09 April 2022 14:50

coredump
Messages: 33
Registered: January 2020
Location: Germany

Member

Hi Andrew,
lynchaj wrote on Wed, 06 April 2022 13:01

Hi
First item is replacing the uPD7220 (NMOS) with uPD72020 (CMOS). Originally I was hoping to do this purely for reduced power usage but it also appears there are some beneficial software improvements as well. Does anyone have experience in replacing the uPD7220 with uPD72020 and/or programming it? They appear to be pin compatible and software compatible but the uPD72020 is more recent and has some improvements.

from my point of view here the advantages of the 72020 are:
1) ability to handle dual ported DRAMs like the µpD41264
2) 2xCCLK of 8MHz
3) (less important, would disallow DMA) larger address range of 2MB

Since the old 7220 usually requires flashless mode the dual ported DRAMs would allow an increase of (nearly..) x4 in drawing speed.
Doubling 2xCCLK obviously gives another x2.
If You intend to connect it to a Monitor made somewhere in this millennium, a pixel clock up to 32MHz could be used.
So all together an increase of x10 in drawing speed should be possible.
With much less afford and much more effect than a shared memory architecture.

Best Regards
Detlef

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Re: uPD7220 vs uPD72020 [message #9858 is a reply to message #9856]

Sun, 10 April 2022 09:48

lynchaj
Messages: 1080
Registered: June 2016

Senior Member

Hi
One of the Z180GDC build and test team installed a uPD72020 instead of an uPD7220A and it seems to work. I have one on the way too so am looking forward to testing with the uPD72020. Assuming it works with the Z180GDC that will become the specified part because it has so many advantages over the older NMOS uPD7220

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