General > General Technical Chat

Identify these weird EPROMs

<< < (5/6) > >>

ieure:

--- Quote from: TheSteve on February 01, 2023, 08:53:58 pm ---I feel like they were probably the worlds first DS/HD (Double Sided High Density) EPROM's.

--- End quote ---

Quad-core EPROMs!

wraper:

--- Quote from: BrianHG on February 02, 2023, 03:37:59 am ---You cheap slow 74LS138 added up to 41ns of propagation delay to what was already a slow 200ns eprom.  How fast was the ' MMI PAL10L8-2ML ' when doing a simple 2 to 4 address decode mux?  IE: only 3 of 8 product terms for each output...  I bet it was a crap load faster... 

--- End quote ---
This PAL has larger propagation delay than 74LS139. If needed faster there were 74/54 S, AS, H, F series too.

--- Quote ---How fast was the ' MMI PAL10L8-2ML ' when doing a simple 2 to 4 address decode mux?
--- End quote ---
Its speed does not depend on what's it's doing as it's a very simple device.

--- Quote ---Also, don't forget you may be also emulating the OE and CE, not just the upper addresses as a control input element.  IE: when programming 1 of 4, you will need to operate the CE while keeping all OEs disabled.  When reading, the OE are preferable for address switching over using the CEs as the CEs do power-down the eprom and slow things down to awaken.  This added switch in functional wiring/control makes a PAL far better suited while you would need some more additional logic ICs to wire all this up.
--- End quote ---
Well, you should switch only either CE or OE, with other connected together between EPROMs and connected to external pin. You can switch OE or CE with 74LS139 and use it's enable pin as external OE or CE.
EDIT: regarding programming while switching OE, not CE for better speed, yes PAL makes sense. For example you could use second half of LS139 connected to CE. However a little bit of additional logic would be needed for enabling all CE outside of programming.

wraper:
BTW I never claimed It cannot possibly be 27256. My argument is that using PAL for that is unnecessary, wasteful and requires more work as you need to program PAL before attaching to the package.

wraper:
While thinking more, I realized there is not enough pins in the package for 27256 having PGM input. And I fail to see how PAL would solve this problem to be able to program 2764 within module.
EDIT: maybe it's what those apparently resistors are for. Maybe a voltage divider from Vpp to PAL input to activate an alternate PGM input mode for CE pin.

amyk:
You're not the only one on the Internet to speak of such a thing: https://forums.arcade-museum.com/threads/show-n-tell-time-take-a-look-mbm2764-20-fujitsu-odds-are-you-never-seen-one-like-this-before.478300/

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod