[Coco] 6809 FPGA

[Dave Philipsen]

Well I can't really explain why you would have noise but it could be 
crosstalk on your wires.  Are you wire-wrapping?

The reason I suggested starting at lower speeds is that any timing quirk 
with the memory will be more likely to be forgiven at the lower clock 
speed.  Originally, one of my boards would only work at slower speeds up 
to 12 MHz until I made some changes.  The DE1 board worked at 25 MHz 
only after I changed some of the chip select logic.  And you will be 
limited by the access time on your RAM chip.

I might have mentioned this before but you might be better of first 
enabling some of the internal memory as RAM.  That way you can get the 
system up and running without any external RAM at first and then you can 
try to enable it later.  Another advantage is that the internal memory 
should be able to run at any speed without problem.

The EP2C5T that Grant used only has 13K bytes of internal memory for 
program RAM, display /attribute RAM, font ROM, and program ROM.  But 
your DE0 has 56K bytes.  You could allocate 8K for the BASIC ROM, 5K for 
the display, and still have 43K left over for program RAM. That's more 
than you'd get with a 32k RAM chip. And, you'll get the project up and 
running faster because there's less chance for error when you use the 
internal memory.


Dave


On 9/10/2015 11:43 PM, Bill Nobel wrote:
> Well I have noticed so far, that I get less noise on the VGA the faster I go.  I am using a VGA breakout from Sparkfun electronics, that has 270ohm resistors instead of Grants spec.
>>   Also, just go ahead and set the CPU speed down to the the lowest speed at first.  I think that's 1 MHz.  When the board comes up then you can experiment with increasing it.
>>
> I found for the noise I get on the vga I get less the faster I go.
>
> I don’t know why, but now I don’t have those messages on compile for the ROM.  I was playing with timing on VGA for cleaning up the noise, but those messages disappeared.
>
> Bill Nobel
>
>> Cut and paste the "rollover" warnings and send them to us.  That doesn't ring a bell.
>>
>> Dave Philipsen
>>
>>
>> On 9/10/2015 10:55 PM, Dave Philipsen wrote:
>>> Oh, and the 3.3v levels are actually TTL.  They're just a low-voltage version of standard 5v TTL.  Some 5v stuff will actually work with 3.3v signals apparently but you probably would get into trouble driving any 3.3v (LVTTL) with 5v signals.
>>>
>>> Personally I would recommend the AS6C4008-55PCN <https://www.mouser.com/Search/ProductDetail.aspx?R=AS6C4008-55PCNvirtualkey56240000virtualkey913-AS6C4008-55PCN> SRAM. It's 512K, 3.3v - 5v tolerant, and only costs around $4.50.
>>>
>>> Dave Philipsen
>>>
>>> On 9/10/2015 10:36 PM, Dave Philipsen wrote:
>>>>
>>>> On 9/10/2015 10:12 PM, Bill Nobel wrote:
>>>>> Hey all,  I (as some of you know) have been trying to get Grant Searles project running on a DE0 Nano. I have made some good advancements (Many, many thanks greatly to Roger Taylor and Dave Philipsen).
>>>>>
>>>>> But I need a little help again.  I took Rogers suggestion of updating my Quartus ii software to 15.0 and things did dramatically change.  I now have a flashing cursor in the top left corner (which should be there upon init of the VGA circuit).  I do have what seems like a little sync noise on the background (nothing serious).  I could post a pic, but I don’t want to clog the list.  This is all I get once I program the DE0 with Grants code.
>>>>>
>>>>> I think there is a problem with my selection of the external RAM chip (and or the pins I chose to drive it, it is all on GPIO-0) I am using a Hitachi 628128 128k SRAM (only using 64k).  I am personally thinking, looking at the data sheet for the RAM, that it might not handle 3.3v CMOS levels good enough.  Am I correct?
>>>> Yep, that's a 5v SRAM.  And my guess is you need a 3.3v SRAM.  I am not positive on what the DE0 does for I/O but if it's like the DE1 then it's 3.3v.
>>>>
>>>>
>>>>> Also, I do think something is wrong in the ROM code, it does compile, but I see in the reports, that there is a rollover in the intel HEX code and I don’t see any LU’s allocated for it in the compile reports.  I get a total of 44 warnings (most are for pin assignments I have not assigned yet).
>>>> Not sure what you mean by rollover.
>>>>
>>>>> I also see a discrepancy on the pin planner versus the assignment editor, The pins are duplicated in the assignment editor, one set stating my location assignments, the other just stating location.  Is this normal?
>>>> You could have some pins duplicated in the assignment editor if one line assigns the signal to a pin and another line defines something else about the pin like whether it has a weak pull-up resistor attached to it for example.
>>>>
>>>>> Bill Nobel
>>>>>
>>>>>
>>>> Dave Philipsen
>>>>
>>>>
>>>> ---
>>>> This email has been checked for viruses by Avast antivirus software.
>>>> https://www.avast.com/antivirus
>>>>
>>>>
>>>
>>>
>>> ---
>>> This email has been checked for viruses by Avast antivirus software.
>>> https://www.avast.com/antivirus
>>>
>>
>> ---
>> This email has been checked for viruses by Avast antivirus software.
>> https://www.avast.com/antivirus <https://www.avast.com/antivirus>
>>
>>
>> -- 
>> Coco mailing list
>> Coco at maltedmedia.com <mailto:Coco at maltedmedia.com>
>> https://pairlist5.pair.net/mailman/listinfo/coco <https://pairlist5.pair.net/mailman/listinfo/coco>


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus