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TI-99/4A HARDWARE

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#176 gregallenwarner OFFLINE  

gregallenwarner

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Posted Tue Nov 4, 2014 11:30 AM

Sounds great! Thanks! I'll check Thierry's site to see if I'm lacking anything in the ol' parts bin. I think I have a 74LS612 stashed away somewhere from a long-ago abandoned attempt to build a SAMS clone.

If I might ask, where are you sourcing your 612 memory mappers from? As I recall, I had a difficult time finding mine.

Also, I have another question. Thierry's site shows that the HAMS can be used with up to 16 meg of SRAM chips. Considering the cost of purchasing that many chips, does your board have any provision for smaller configurations? For example, can I install 4 meg worth of chips, and configure the board appropriately to use that particular memory size?

#177 Ksarul OFFLINE  

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Posted Tue Nov 4, 2014 1:47 PM

The board works in any configuration from 4 to 16 MB--you just populate what you need to initially and go from there. I get my 612s from Unicorn Electronics. or occasionally, from eBay sellers that I've used in the past and that generally provide genuine chips. Note that two of the chips on the board are a bit weird: 74ABT244 and 74ABT245. I've got a small stock of both of them, so I'll try and make sure I include one of each with the card. Note also that one of the other chips comes in both skinny DIP and wide DIP--Thierry planned for the skinny DIP version (bad idea, as they are really hard to source). I made the board so that you can use whichever type you find--just put the right socket in and go.



#178 gregallenwarner OFFLINE  

gregallenwarner

    Chopper Commander

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Posted Tue Nov 4, 2014 1:53 PM

What's the key to those 74ABT series chips? Are those different from standard 74LS or 74HCT series?

#179 Ksarul OFFLINE  

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Posted Tue Nov 4, 2014 1:58 PM

They are definitely necessary if you plan to eventually populate the board beyond 4MB, as they are better at driving a large number of chips than the others are--and if you end up with the full four layers of chips, that is a lot of chips to drive. . .the ABT chips were a recommendation in Thierry's documentation to minimize problems on the larger boards.



#180 gregallenwarner OFFLINE  

gregallenwarner

    Chopper Commander

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Posted Tue Nov 4, 2014 2:00 PM

Ah, gotcha. Makes sense.

#181 OLD CS1 OFFLINE  

OLD CS1

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Posted Tue Nov 4, 2014 2:35 PM

Is there any compelling reason to not use SIMMs in RAM cards for the TI?  Are the RAM chips we can get newer production?  I know there are hoards of SIMMs around (I happen to have a couple hundred, unless I gave them away, already.)



#182 gregallenwarner OFFLINE  

gregallenwarner

    Chopper Commander

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Posted Tue Nov 4, 2014 3:26 PM

SIMM's are dynamic RAM, or SDRAM (Synchronous Dynamic RAM) to be precise. They require some controller circuitry to dynamically refresh the cells. That would be a lot more complex of a circuit, since static RAM's can basically interface directly with the PEB Bus.

#183 OLD CS1 OFFLINE  

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Posted Tue Nov 4, 2014 4:28 PM

SIMM's are dynamic RAM, or SDRAM (Synchronous Dynamic RAM) to be precise. They require some controller circuitry to dynamically refresh the cells. That would be a lot more complex of a circuit, since static RAM's can basically interface directly with the PEB Bus.

 

Seems compelling enough.



#184 mizapf OFFLINE  

mizapf

    River Patroller

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Posted Tue Nov 4, 2014 4:56 PM

This is also one reason that VRAM and CPU RAM are distinct memory areas - the VDP uses DRAM, and it has an integrated DRAM controller which allows for refreshing the DRAM. If you would try to open VRAM to the CPU, you would have to employ some synchronisation mechanism so that memory is not accessed during the refresh cycle.



#185 Tursi OFFLINE  

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Posted Wed Nov 5, 2014 1:11 PM

The PEB 32k card uses DRAM and has an onboard refresh circuit, it's not really that hard. But SRAM doesn't require anything but a select line. ;)



#186 vectrexroli OFFLINE  

vectrexroli

    Moonsweeper

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Posted Sat Nov 29, 2014 2:53 PM

I would be also interested in such a board.



#187 RXB OFFLINE  

RXB

    River Patroller

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Posted Sat Nov 29, 2014 9:05 PM

Normal 32K compared to SAMs 1Meg is laughable performance differences.

 

Using SAMs I have many demos that make  RXB screaming fast compared to standard 32K.

 

If you run this in normal 32K vs SAMs you will see a marked difference have not timed it but from SCSI it is considerably faster as the only timed test I ever ran.

 

 

 

By the way show me any other XB made with the built in support for SAMs!

(Or RAMDISK, SCSI or other devices.)


Edited by RXB, Sat Nov 29, 2014 9:09 PM.


#188 UKRetrogamer OFFLINE  

UKRetrogamer

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Posted Mon Dec 1, 2014 6:55 AM

Please add me. Shipping to the UK. Thanks.



#189 gregallenwarner OFFLINE  

gregallenwarner

    Chopper Commander

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Posted Thu Dec 4, 2014 9:00 AM

Just an update to everybody who's wondering where I'm at with this project:

 

I've gotten the revised boards in; I had to add a buffer chip between the PEB bus and the speech synth, to see if that would solve my issues with my first prototype. However, my forgetfulness bit me when I took a look through my inventory; I had spec'd out the chip to use way back when I did the redesign, but I realized I had failed to order any. Anyway, I got my parts on order, so I should be able to assemble the 2nd round of prototypes soon as they come in.

 

I think I'm going to create a new official thread for this board whenever it comes time for the big run, to give everybody a chance to lock in their order, but I've got everyone's name written down who's expressed interest either on this thread or by PM, so I can be sure to make enough for everybody. The number is currently over 30 so far! I can't thank everybody enough for their interest in my project!



#190 --- Ω --- OFFLINE  

--- Ω ---

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Posted Tue Dec 12, 2017 9:38 AM

Is this now considered an abandoned project?



#191 abecedarian OFFLINE  

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Posted Tue Dec 12, 2017 1:23 PM

Is this now considered an abandoned project?

 

If so, unfortunate as I was just getting interested. :(







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