512k Sram card....possible?

[danwinslow]

This interesting device :

 

http://www.parallax.com/Store/Microcontrol...e%2cProductName

 

Is a stand-alone 512k SRAM card that is designed to be used (by a device) with an 8 bit data path and 64k addressable. It seems very interesting...I was wondering if any of you hardware types think it could be interfaced, either via a cartridge or maybe the PBI...or maybe even joystick ports. We would want to map it into the normal scheme of banking if possible, via PIA pins etc. I think I understand the programmatical access and could write an atari-side driver, but I don't have a lot of knowledge about how the hardware might work. If I had a way to drive the states on the control pins by writing to locations I think I could do most of whats needed in software.

 

From the manual ( http://www.parallax.com/Portals/0/Download...v1_0_online.pdf )

There is absolutely no reason why you can’t use the HX512 with other devices or with other microcontroller based

products that you want to add external memory to. All you really need is the 20-pin edge card interface and you are up

and running. The HX512 card’s interface is mechanically 20-contacts with 10-contacts per side and 0.1” spacing between

contact centers. The depth the card inserts into the edge connector is approximately 5/16”. The pins are numbered from 1

to 10, right to left (pin 1 is on the far right with the card facing you), and pins 11-20 on the back side numbered left to right.

Figure 38.0 shows a top view of the expansion port on the HYDRA for reference and Figure 39.0 shows the simple circuit

diagram of the interface.

[Rybags]

At that price, there's probably plenty of better alternative storage solutions like existing SRAM cartridge projects etc.

 

The point of interest with this one though is the CPLD. Reprogramming it might make for some sort of useful slave processor device.

 

Interfacing? IMO the best solution might be just via cart, addressable through the $D5xx page.

 

I've not looked at the manual there - 20 pins seems a bit excessive for something that is essentially only a sequential access by byte setup.

[danwinslow]

I like the cart idea as well. The problem is that I don't know how to interface electrically. I can see buying the 20-pin card interface, and I can get a cartridge connector/bare pcb but I don't know what to do hardware-wise after that. The mapping from the internal atari $D5xx to the cartridge pinout I am sure is documented well and I can probably understand it with some work...but crossing from that in electrical terms onto the 20 pins of the Sram card I don't know how to approach. I assume its more complicated than just soldering the lines together in some fashion.

[Rybags]

Another consideration - what voltages does this thing expect? Is it legacy 5V, or something more modern/lower.

 

I'd be looking at this thing anyway from a usefullness POV so far as what you might be able to get the CPLD to do for you.

 

Otherwise, you're probably way better off just getting one of the 512K SRAM carts that does 8K banking or whatever within the $A000-BFFF address space.

[danwinslow]

People talk about the SRAM carts and so forth, but I have yet to see one or any plans for one. Maybe I'm out of the loop, I dunno. At any rate I'd really like to try to interface something like this myself. The object would be as much to learn as it would be to wind up with a SRAM cart. (And I am also interested in the CPLD...they have a programmer for it as well thats fairly cheap) But, I can't ever seem to get a handle on what needs to be done electrically though. Nobody even suggests how to start usually...not complaining, its just frustrating. The voltages I think are 3.3 volts on the card edge connector. I'm not sure, but lets just say thats true. What does that mean? The atari is 5 volt, right? So what needs to be done to bridge the two? I mean generally, I'm not expecting people to to explain a very large subject to me. Just some hints maybe, or some places to look. Maybe a book reccomendation or something.

[candle]

if this is for hydra platform, then propeller (8 core cpu running hydra) is 3v3 device...

there was sram based cart called "ramcart" sold in poland some time ago, in early 90's

basically it was sram chip, 3v lithion battery for backup and few chips of glue logic - nothing fancy, but it workedd!

[danwinslow]

Hi Candle. Yah its the hydra, which looks like a neat system on its own. So its 3.3 to 5 (?) I guess on the atari. You wouldnt have any locations for some instructions or diagrams for the ram cart would you?

 

I just need to get my head into how to connect the hardware up. It can't be that hard, been a programmer for years and years so I shoudl be able to handle it once I learn where to start. I bought a microcontroller kit ( its a basic stamp ) and a book of educational projects, so I can at least start to get some idea.

[candle]

i would

http://tajemnice.atari8.info/8_92/8_92_djvu.html, page 13

http://tajemnice.atari8.info/11-12_92/11-12_92_djvu.html page 9

and there should be programs for it (dos handler, so it could be seen as floppy disk, etc)

should be quite simple, this cart just maps part of memory onto standard cart locations, and uses additional register for switching banks

[ijor]

The voltages I think are 3.3 volts on the card edge connector. I'm not sure, but lets just say thats true. What does that mean? The atari is 5 volt, right? So what needs to be done to bridge the two?

 

When you connect a 5V device to a 3V (that is not 5V tolerant), you need voltage level translators. The main problem is that the 3V device would be (sooner or later) damaged if it would get 5V.

 

There are different ways to implement voltage level translation. It depends on the signals being bidirectional or not, frequency, etc.

 

Note that some 3V devices are 5V tolerant. And actually, using 5V tolerant buffers is a very common method for implementing voltage level translation.

Edited February 5, 2009 by ijor

[danwinslow]

Thanks Candle Can't get to them now, but I'll check at home. Hope they are in english or german

 

Ijor - Mmm..so the buffer would be some kind of 5v tolerant chip in between?

[ijor]

Ijor - Mmm..so the buffer would be some kind of 5v tolerant chip in between?

 

If the signal is not bidirectional, going from the 5V to the 3V device; then yes, a simple 3V buffer that is 5V volt tolerant (such as the LVT244) in between would be a good solution. For the other way around, from 3V to 5V, and as long as the 5V device uses TTL levels (as is the case in the A8), then no voltage level translation is required.

 

But I assume here that at least some of the signals are bi-directional. Then you can't use a simple buffer because those buffers are not bi-directional. You need a more complex level translator, such as a transciever; or implement the translation with discrete components, such as diodes and resistors.

[danwinslow]

I think this ( discrete ) is what they are talking about here :

http://www.sparkfun.com/commerce/tutorial_...tutorials_id=65

[danwinslow]

Candle, I can't get anything from those pages. There's some kind of wierd plug-in that niether firefox nor IE can seem to find. EVen if i could, it would seem that it's in a language thats not english and not german..I'd guess polish maybe? So they are of no use to me, but thanks anyway.

[candle]

pretty strange - as i have this installed under firefox

this is called dejavu by lizardtech if memory serves

and... make little prayer to any known god - texts are in polish

hope you'll figure something out from schematics, if not, ask specific questions and i'll try to answer

[HiassofT]

If I deciphered the picture correctly, the CPLD on this board is a Lattice 4064V. This is a 5V tolerant 3.3V device and you can connect it directly to your Atari.

 

But: be careful. If the databus isn't routed through the CPLD but instead directly connected to the RAM chips, it might fail and even damage the RAM (if it's not 5V tolerant). In this case you would need a bus transceiver to adjust voltage levels.

 

Another thing: don't expect to get this working on all Ataris. A lot of the Ataris suffer from timing problems (falling edge of PHI2 is too late) and modern chips (like this CPLD) are fast enough to be affected by this issue.

 

If you like to get into the interesting world of CPLDs you could also start from scratch: Buy a Lattice Mach 4A5 (5V device), a Xilinx XC95xx (5V) or a Xilinx XC95xxXL (3.3V) device in PLCC, plus a PLCC socket and solder it onto a breadboard. If you use a 3.3V device you also need a 3.3V voltage regulator (connect this to VCC of the CPLD and +5V to VCCIO of the CPLD).

 

The development software (ispLever classic or Xilinx webpack) is freely available and the simplest JTAG interface needed to program the CPLD consists of just 5 resistors and a 25pin SUB-D connector for the PC parallel port (slightly better designs add a line transceiver, but the very simple interface also works fine if the cables are short).

 

so long,

 

Hias

[candle]

i just wonder, would be there any intrest in 1mb sram cart (8k banked throuhgt register on d4xx page) with battery backup and flash backup capability?

estimated cost - $45, maybe less

flash would be capable of storing up to 4 complete images of cart (4mbyte of data)

[danwinslow]

I'd buy a couple.

[+bf2k+]

i just wonder, would be there any intrest in 1mb sram cart (8k banked throuhgt register on d4xx page) with battery backup and flash backup capability?

estimated cost - $45, maybe less

flash would be capable of storing up to 4 complete images of cart (4mbyte of data)

 

I'd buy one.

[GameEngine]

i just wonder, would be there any intrest in 1mb sram cart (8k banked throuhgt register on d4xx page) with battery backup and flash backup capability?

estimated cost - $45, maybe less

flash would be capable of storing up to 4 complete images of cart (4mbyte of data)

 

No, unless it is superset of cartridge by Raster and Bob!k:

http://raster.infos.cz/atari/hw/ramcart/ramcart.htm