8085A CPU!

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norberto.collado koyado.com

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Mar 18, 2023, 2:20:02 AM3/18/23
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Scott,

 

As I have several 8085A CPU’s, I will like to take your design + GALS and use the 8080A board template (picture attached) and replaced the 8080A CPU with the 8085A CPU + your GAL logic to complete the H8 CPU family; 8080A -> 8085A -> Z80 -> Z180 with the same I/O’s interface.

 

Can you send me the 8085A schematics in pdf and the GALS equations?

 

Thanks,

Norberto

 

Scott Baker

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Mar 18, 2023, 11:40:21 AM3/18/23
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Yeah, I will get them published this weekend. I made another respin of the board and received it last week -- I just need to build it now to verify I finally have everything right. Should be able to build it up today.

Scott

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norberto.collado koyado.com

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Mar 18, 2023, 3:22:57 PM3/18/23
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No rush and thank you!

 

😊

Lee Hart

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Mar 25, 2023, 4:38:30 PM3/25/23
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This gave me a (silly?) idea. NEC made a CPU chip (the V20) that has *both* the 8088 and
8080 instruction sets. The hardware interface is just like an 8088. The software has instructions
to switch it between 8088 and 8080 modes.

Would it be possible to design an H8 CPU board with this chip? If so, it could be switched to
8080 mode at reset to run normal H8 software. But programs could switch it to 8088 mode
for more "fun". :-)

Lee

Joseph Travis

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Mar 25, 2023, 4:39:56 PM3/25/23
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I agree!

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smb...@gmail.com

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Mar 25, 2023, 4:46:07 PM3/25/23
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One of the things on my mind was an 8085/8088 or 8085/8086 board. There were numerous examples of such things back in the s-100 space. There were even 8085/80286 if I recall correctly.

The v20, with just one ic, would be much easier. My only concern is that it probably boots in 8088 mode and you’d have to switch it to 8080 mode for the boot loader / monitor. So maybe a few boot loader/monitor changes…

Sent from my iPhone

On Mar 25, 2023, at 1:39 PM, Joseph Travis <jtravi...@gmail.com> wrote:


I agree!

On Sat, Mar 25, 2023, 4:38 PM Lee Hart <electr...@gmail.com> wrote:
This gave me a (silly?) idea. NEC made a CPU chip (the V20) that has *both* the 8088 and
8080 instruction sets. The hardware interface is just like an 8088. The software has instructions
to switch it between 8088 and 8080 modes.

Would it be possible to design an H8 CPU board with this chip? If so, it could be switched to
8080 mode at reset to run normal H8 software. But programs could switch it to 8088 mode
for more "fun". :-)

Lee

On Sat, Mar 18, 2023 at 2:22 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

No rush and thank you!

 

😊

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Scott Baker
Sent: Saturday, March 18, 2023 8:40 AM
To: se...@googlegroups.com
Subject: Re: [sebhc] 8085A CPU!

 

Yeah, I will get them published this weekend. I made another respin of the board and received it last week -- I just need to build it now to verify I finally have everything right. Should be able to build it up today.

 

Scott

 

On Fri, Mar 17, 2023 at 11:20 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Scott,

 

As I have several 8085A CPU’s, I will like to take your design + GALS and use the 8080A board template (picture attached) and replaced the 8080A CPU with the 8085A CPU + your GAL logic to complete the H8 CPU family; 8080A -> 8085A -> Z80 -> Z180 with the same I/O’s interface.

 

Can you send me the 8085A schematics in pdf and the GALS equations?

 

Thanks,

Norberto

 

<image001.png>

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Joseph Travis

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Mar 25, 2023, 5:06:59 PM3/25/23
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You're correct Scott and as my memory serves, it is a 3 byte instruction to switch to 8080 mode.

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Steven Feinsmith

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Mar 25, 2023, 5:10:42 PM3/25/23
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I was familiar with NEC V20 many years ago. My Heath/Zenith 120 is running with 8088 and 8085. I replaced the 8088 with the V20. It worked well. I want you to be aware of the V20 microprocessor. The V20 can be used on the H8 system because it remains 8-bit hardware while the internal processor handle 16-bit (fetches 8-bit by two times.) One thing with the V20's instruction set architecture is similar to that of the Intel 80188 with some extensions—also, the segment offset where an emulation of an Intel 8080.
Unfortunately, the source listing for the H8 will have to be re-write to enable the 8088 functions. It needs to create a new generation of H8 board with V20 and use the source listing from the H/Z 100 series (not H/Z-100 PC because they were different.) I have the source listing and hardware schematic on my shelf. One thing to keep in mind, it will not run with PC DOS unless the hardware has to install to support the IBM PC software. I have an S-100 board called the S-100 MS-DOS support board. It may be possible to modify it into the H8.
Developing that kind of hardware and creating a new source listing will be a big challenge.

Steven







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steve shumaker

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Mar 25, 2023, 5:25:02 PM3/25/23
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ya..  that was an AWESOME chip!

steve

Glenn Roberts

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Mar 25, 2023, 5:47:56 PM3/25/23
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Speaking of the Z100, the CP/M85 BIOS is mostly written in 8088 assembly. BIOS calls switch the CPU board to the 8088 processor to do the work. The 8088 can access RAM that the 8085 can’t see. This has the effect of speeding up the BIOS and making a small RAM footprint for the BIOS in the 8085’s 64K… some of the value adds of a dual processor.

Sent from my iPad

On Mar 25, 2023, at 5:25 PM, steve shumaker <shum...@att.net> wrote:

 ya..  that was an AWESOME chip!
I agree!

<image001.png>

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norberto.collado koyado.com

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Mar 25, 2023, 9:48:34 PM3/25/23
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Where you can buy such V20 ic???
From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Glenn Roberts <glenn.f...@gmail.com>
Sent: Saturday, March 25, 2023 2:47:42 PM
To: se...@googlegroups.com <se...@googlegroups.com>

Joseph Travis

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Mar 25, 2023, 11:09:11 PM3/25/23
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I have several 10 MHz V20 CPUs in my inventory.

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Peter Higgins

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Mar 26, 2023, 11:58:08 AM3/26/23
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The primary source for NEC V20 chips is eBay. For some insight see:

In an internet search for this part you can get more hits by looking for the V20 by its NEC part number D70108x, where x is most commonly the C or D versions. There is also a 16MHz D70108HCZ version.

smb...@gmail.com

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Mar 26, 2023, 12:04:30 PM3/26/23
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If memory serves, I used a NEC V20 in my Tandy 1000 back in the day. A popular upgrade, offering both increased clock speed and better performance per clock cycle.

Probably have one install in my Sergey Xi8088 at the moment.

A good and popular IC.

Scott

Steven Hirsch

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Mar 26, 2023, 1:53:19 PM3/26/23
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On 3/26/23 11:58, Peter Higgins wrote:
> The primary source for NEC V20 chips is eBay. For some insight see:
> https://forum.vcfed.org/index.php?threads/can-i-trust-these-listings-for-nec-v20%E2%80%99s.1241877/
>

There are new ones (5 MHz, I believe) available here:

https://www.arcadecomponents.com/catalog/item/2243545/10411091.htm

steve shumaker

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Mar 26, 2023, 8:14:58 PM3/26/23
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Actually Google says there are a couple (non EBay) vendors still
offering (or at least listing) the 40pin DIP up to 10MHz - there's even
a PLCC version running at 16MHz!

Steve
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