C64 Cartridge Port Write Timing Issues

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C64 Cartridge Port Write Timing Issues

Jim Brain

I've been trying to help a couple of folks create a cart for game development.  Since I've no desire to re-invent the wheel, I thought using the EasyFlash 1 design would be ideal, but I see many folks complain that the EF1 design won't flash on some C64 models:


PAL 250466 ( b-3) FAIL

PAL 250469 (E) PASS

PAL 310378 (128D) FAIL

A couple questions:


Since it appears EasyFlash might have an issue, is there a reference design for writing RAM/ROM on the cart port I should consider for designs?

Does anyone else have any insight on the EF1 writing issues?  The design looks straightforward, and I know skoe and Martin (I think) worked on shortening and delaying the write strobe so that the design would meet setup and hold time constraints for external writes.

Barring either of those, any guidance on where to start debugging?

My goal is to obtain a "reference" design that can be posted to zimmers or somewhere, so folks have a reasonable implementation they can depend on for external RAM/ROM carts.

I know EF3 does not have the issue, but it's a large CPLD, and it seems like writing to FLASH ROM or SRAM on the external bus should be something that is possible with standard TTL parts.

Jim


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Jim Brain
[hidden email] 
www.jbrain.com
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RE: C64 Cartridge Port Write Timing Issues

Jeremy-2
Jim, why do you need a game cart when you have so many utility carts to choose from. Why not use a rom/ram like ram dose that I believe you still own the rights to?

Utility carts use less ram and rom in then game cartridges??? (In my own opinion?)

Jeremy 



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-------- Original message --------
From: Jim Brain <[hidden email]>
Date: 6/11/2017 7:12 PM (GMT-08:00)
Subject: C64 Cartridge Port Write Timing Issues

I've been trying to help a couple of folks create a cart for game development.  Since I've no desire to re-invent the wheel, I thought using the EasyFlash 1 design would be ideal, but I see many folks complain that the EF1 design won't flash on some C64 models:


PAL 250466 ( b-3) FAIL

PAL 250469 (E) PASS

PAL 310378 (128D) FAIL

A couple questions:


Since it appears EasyFlash might have an issue, is there a reference design for writing RAM/ROM on the cart port I should consider for designs?

Does anyone else have any insight on the EF1 writing issues?  The design looks straightforward, and I know skoe and Martin (I think) worked on shortening and delaying the write strobe so that the design would meet setup and hold time constraints for external writes.

Barring either of those, any guidance on where to start debugging?

My goal is to obtain a "reference" design that can be posted to zimmers or somewhere, so folks have a reasonable implementation they can depend on for external RAM/ROM carts.

I know EF3 does not have the issue, but it's a large CPLD, and it seems like writing to FLASH ROM or SRAM on the external bus should be something that is possible with standard TTL parts.

Jim


-- 
Jim Brain
[hidden email] 
www.jbrain.com
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RE: C64 Cartridge Port Write Timing Issues

Jeremy-2
In reply to this post by Jim Brain
Just reread your post about the ef1 and constraints of it for port writes? 
Is it a timing frequency shift? Could you check that for the ntsc and pal operate on different frequencies not just the TV portion but also the writing and read for external roms and ram carts. Jeremy



Sent from my T-Mobile 4G LTE Device
-------- Original message --------
From: Jim Brain <[hidden email]>
Date: 6/11/2017 7:12 PM (GMT-08:00)
Subject: C64 Cartridge Port Write Timing Issues

I've been trying to help a couple of folks create a cart for game development.  Since I've no desire to re-invent the wheel, I thought using the EasyFlash 1 design would be ideal, but I see many folks complain that the EF1 design won't flash on some C64 models:


PAL 250466 ( b-3) FAIL

PAL 250469 (E) PASS

PAL 310378 (128D) FAIL

A couple questions:


Since it appears EasyFlash might have an issue, is there a reference design for writing RAM/ROM on the cart port I should consider for designs?

Does anyone else have any insight on the EF1 writing issues?  The design looks straightforward, and I know skoe and Martin (I think) worked on shortening and delaying the write strobe so that the design would meet setup and hold time constraints for external writes.

Barring either of those, any guidance on where to start debugging?

My goal is to obtain a "reference" design that can be posted to zimmers or somewhere, so folks have a reasonable implementation they can depend on for external RAM/ROM carts.

I know EF3 does not have the issue, but it's a large CPLD, and it seems like writing to FLASH ROM or SRAM on the external bus should be something that is possible with standard TTL parts.

Jim


-- 
Jim Brain
[hidden email] 
www.jbrain.com
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Re: C64 Cartridge Port Write Timing Issues

Jim Brain
On 6/12/2017 4:09 PM, earth1dome1 wrote:
> Just reread your post about the ef1 and constraints of it for port
> writes?
> Is it a timing frequency shift? Could you check that for the ntsc and
> pal operate on different frequencies not just the TV portion but also
> the writing and read for external roms and ram carts. Jeremy
I am soldering up a unit here to test on NTSC, but I only have one PAL
unit to test, so if I can't replicate the issue on NTSC, I am hoping
this single PAL option will generate the issue.

Jim


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