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Post by minsoft on Mar 15, 2021 8:15:05 GMT -5
I have a cart with an eprom ZIF socket for testing, which has a DS2430A and resistor wired up for save data. I'm using Alex Herberts driver for the software side.
It works perfectly when using UV erasable eproms, eg AMD AM27C256. However I recently bought a few 'one time' non-erasable eproms to try (Cypress CY27C256), and with these, the (32k) game I am testing does some strange things (eg flickering vectors) and after a while crashes (black screen, stuck sounds). The same game with save data code disabled works fine on these eproms however.
Does anyone know why this might be? Perhaps just a case where the Cypress eproms are not a good match for the rest of the hardware?
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Post by minsoft on May 19, 2021 8:27:21 GMT -5
I shouldn't have referred to the Cypress one-time programmable device as an 'eprom', it's just a prom I suppose.
I haven't got to the bottom of this. But since all the UV-erasable eproms I've tried work ok, I will stick with those.
Maybe the Cypress proms I have could be useful for games/code which do not have a save data feature.
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Post by gauze on May 21, 2021 9:59:28 GMT -5
I do not known but I'd check pin assignments I guess. it sounds like something is yacking on "the bus" when it shouldn't be maybe.
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Post by minsoft on May 24, 2021 7:05:19 GMT -5
I do not known but I'd check pin assignments I guess. it sounds like something is yacking on "the bus" when it shouldn't be maybe. Thanks. I did check the pinouts and they appear the same as a regular 27C256 uv eprom. Using the exact same PCB with eeprom to test the two so that is consistent.
My electronic skills are not sufficient to work out what's going on, so I'll just use the uv eproms.
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Post by kokovec on May 24, 2021 18:35:53 GMT -5
Do you know which version of the CY27C256 you purchased? It comes in different access time speeds (in ns). I found there's a sweet spot when it comes to access times and avoiding CPU bus contention.
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Post by minsoft on May 25, 2021 3:40:31 GMT -5
Do you know which version of the CY27C256 you purchased? It comes in different access time speeds (in ns). I found there's a sweet spot when it comes to access times and avoiding CPU bus contention. Thanks, that would make sense...
It is marked CY27C256-120PC. From the following datasheet it shows 'maximum access time' of 120ns:
What do you find to be the sweet spot for access time?
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Post by kokovec on May 25, 2021 11:55:00 GMT -5
I usually stick with 90 or below. However, Cypress chips don't always play nice with the Vectrex. Most Cypress SRAMS/EPROMS have a sleep feature when CE is de-asserted. My guess is that the chip creates an inrush of current that drags down the bus when it wakes up. That is really tough to capture without a good oscilloscope, but could manifest as ringing during signal transitions.
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Post by minsoft on May 27, 2021 4:37:25 GMT -5
I usually stick with 90 or below. However, Cypress chips don't always play nice with the Vectrex. Most Cypress SRAMS/EPROMS have a sleep feature when CE is de-asserted. My guess is that the chip creates an inrush of current that drags down the bus when it wakes up. That is really tough to capture without a good oscilloscope, but could manifest as ringing during signal transitions. Ok thanks, I will just avoid using the Cypress proms.
I checked the UV eproms I have been using, and they all have maximum access time of 200ns (according to data sheet). These seem to work perfectly ok.
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Post by kokovec on May 27, 2021 11:22:19 GMT -5
Ya, it might just be a Cypress issue.
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Post by minsoft on Mar 5, 2022 18:09:30 GMT -5
I checked the UV eproms I have been using, and they all have maximum access time of 200ns (according to data sheet). These seem to work perfectly ok. It seems I spoke too soon...after extensive testing I'm having (less frequent) problems with the UV eproms too. They all have access time of 200+ns so I assume that is the issue. Although the problems occur when there is no loading or saving of data, which seems odd. I'll have to source some eproms with a lower access time to test but it's quite hard to find them. I've seen some 100ns ones but nothing below that yet. Does anyone know a good source?
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Post by binarystar on Mar 30, 2022 6:57:34 GMT -5
Hi, Just posting to say I recently bought the Cypress 200ns OTP EPROMs and have experienced no problems with them. I'm out of 1 wire eproms at the moment so can't test with those but I did write a little Vectrex program to check the eprom contents 1000s of times (I wrote a predictable pattern to the ROM to test against) and experienced no errors in the expected data read by the Vectrex. I wonder if your EPROM burner might not like the slow chips? I'm using a MCUmall GQ-4x4 programmer.
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Post by binarystar on Mar 30, 2022 6:59:21 GMT -5
Could also be something as simple as an intermittent connection on your socketed PCB.
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Post by minsoft on Apr 1, 2022 5:54:08 GMT -5
Hi, Just posting to say I recently bought the Cypress 200ns OTP EPROMs and have experienced no problems with them. I'm out of 1 wire eproms at the moment so can't test with those but I did write a little Vectrex program to check the eprom contents 1000s of times (I wrote a predictable pattern to the ROM to test against) and experienced no errors in the expected data read by the Vectrex. I wonder if your EPROM burner might not like the slow chips? I'm using a MCUmall GQ-4x4 programmer. Thanks for your comment.
The Cypress (as well as all other types I've had problems with) all seem to work perfectly when not combined with the 1 wire eeprom...only with the 1 wire eeprom do they play up.
I'm using a MiniPro programmer and it never fails to program, and always verifies ok. I don't believe the problem is with programming, but some odd dislike between eprom / eeprom.
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Post by minsoft on Apr 1, 2022 5:59:34 GMT -5
Could also be something as simple as an intermittent connection on your socketed PCB. I also don't think that is the case...I have a ZIF socket on my test pcb and it is too much of a coicidence that it *always* works perfectly with my 'known good' eprom type (I have found one which seems reliable), and always plays up with my 'known bad' types. But again, only when used in conjunction with 1 wire eeprom.
I don't understand why the 1 wire eeprom causes an issue because when the crashes/problems happen, is never when load/save data communication is going on.
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Post by gauze on Jul 6, 2022 22:36:34 GMT -5
sorta related has anyone tried DS28E07+ as a drop in replacement for DS243x?
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