Has anyone successfully interfaced a PCF8584 I2C bus controller to a 6502?

I just can't seem to get it to work directly on the 6502 bus.

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Bill

I haven't yet, so unfortunately I can't help you. But I got some to try a while ago and will be following this thread!

When you say "directly", do you mean it worked before when hooked up to a VIA or something? If so I suspect timing issues maybe?

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BB816 Computer YouTube series

Damn i wish i would've known of this thing before i placed my mouser order, i could've made a small expansion card for one of my SBCs to test it out. (sadly the DIP version is not being sold anymore)
The timings appear to be compatible with a 65xx CPU in either 80xx or 68k Mode. (only real different that in 68k mode R/W are combined and 80xx mode has them as seperate RD and WR signals)...
so it should be working assuming that you pull RD/WR low atleast 10ns before pulling CS low (for reading, and opposite for writing). and that you also wait ~150ns before pulling RD/WR or CS back high.

and i do like the fact that it's comaptible with the 8088 as well, so in theory you could put this on an ISA Card and would only need a DOS Driver to make I2C usable on an IBM PC.

I haven't tried it through a VIA yet but I'm guessing you would be able to use it that way in either mode.

I think the problem is the mode switching. It's not explicitly stated in the data sheet, but I think the /WR and /CE are more critical than /WR sometime before /CE. I think they really mean /CE must be asserted after but while /WR is still asserted. With the 6502 you would need to initialize the PCF8584 before you wrote anything anywhere else. It seems to just lock up and not work in either mode and I think that is because if it's exposed to the /WR signal being asserted without the /CE following immediately and while /WR is still asserted it just gets confused. They hint at this when they say the /WR and /CE must be kept stable after a system reset.

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Bill

It does seem a bit murky. And I'm puzzling over the following sentence from Section 6.2 regarding the mode initialization that automatically occurs at startup:
And 68000 mode is what we want (I guess). And, the sentence seems to say that CS needs to be high when R/W falls. So, does that mean that CS needs to be qualified with Phi2? Maybe it's worth trying it that way, if you haven't already. (You haven't shared your schematic.)

BTW, here's the datasheet, for anyone who hasn't seen it yet.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

hey Jeff, I didn't draw up a schematic, but it was trivial.

The device connected straight to the data and address bus with /WR and /CS being fed from a gal. The gal did the decode and also had Phi2 and W/R feeding it so that I could try either method. I was most interested in the 68000 mode and used a scope on /DTACK to see if it got asserted, which my reading of the datasheet tells me it should be asserted once 68000 mode is entered. Yes, I did qualify /CE with Phi2. No luck.

Of course, it could be a dead chip, but I do have 2 of them and neither gave me the result I expected. They could also both be phonies as I got them from eBay. Unfortunately I was not able to find the PDIP version anywhere else at the time.

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Bill

And during this test the PCF8584's R/W input was simply seeing a copy of the CPU's R/W signal, is that right? Just checking.

Maybe your path of least resistance is to give up on 68xxx mode and shoot for 80xx mode instead (which is mentioned as the default for the PCF8584). Since you have the GAL there, perhaps it wouldn't take much to generate separate /RD and /WR strobes.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Yes. W/R without qualifying.

I could try the 80XX mode I guess. The computers I'm trying it on both create qualified /WR and /RD signals anyway..

I want to set up a test jig for testing random ICs for those computers anyway. The PCF8584 can be my first test case.

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Bill

I have DIP version of PCF8584 and tested it on a RC2014 prototype board (Z80 timing). I had it talked successfully to a serial EEPROM (AT24C256). My problem with PCF8584 is it is too slow--100Kb/s max. 14MHz 6502 can bit bang I2C faster than PCF8584. I bit-bang BadApple! video to I2C 128x64 OLED display at the rate of 31mS per 1K image which is 300Kb/s data rate.
Bill

See here http://www.6502.org/users/andre/csa/scsi/index.html

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/

Thanks Andre. I notice though the you tie pin 16 to Vcc. According to the datasheet that becomes the /DTACK output in 68K mode with an open drain. Things are working okay that way? I'm guessing 2K-4K7 resistor might be a better choice??

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Bill

Hm, if that is so, probably a good idea

Haven't really tested it that hard I have to admit. Never really found a good use case for i2c as opposed to more accessible spi.

André

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I knew someone would chime in

As a hobbyist 15 years ago with prices of 10+€ for a single controller and general high prices compared to simple TTL shift registers there was just no motivation for me. I even added the two lines on my bus backplane, but never really used it.

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?