| Author |
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Bob
Guest
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 Posted:
Sat Dec 17, 2005 5:15 pm Post subject:
Re: 8051/2 data and iram memory question |
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Nappy wrote:
| Quote: | a simple 1 minute google will turn up all the information you will ever need
to work with any 8051 on the planet.
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A one minute Google search may turn up a datasheet for any 8051
on the planet. But those datasheets will certainly not contain *all*
the information you will need. I have seen very few datasheets that
didn't contain errors, omissions and ambiguities. |
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Bob
Guest
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| Posted:
Sat Dec 17, 2005 5:15 pm Post subject:
Re: 8051/2 data and iram memory question |
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Meindert Sprang wrote:
| Quote: | "Bob" <bob3635x@yahoo.com> wrote in message
I don't think so. The original 8051 didn't even have internal iRAM.
Well, maybe you mean something different with IRAM, but there is the
internal data ram on the '51, which is 128 bytes in the 8031/51.
And my compiler calls that idata, as opposed to xdata for the external data
ram.
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Sorry, maybe I should have spelled out the acronym. I was
assuming that iRAM meant "instruction RAM", but maybe others
were using it as a synonym for "idata" (internal data RAM).
In that light, what you were saying makes a lot more sense
to me now.
On the original 8051, starting at address zero, it has 128
bytes of data. But also at address zero, it has ROM
containing instructions. The original 8051 uses a Harvard
Archtecture for internal memory, so these are separate
address spaces.
Some 8051 derivatives replace the instruction ROM with RAM.
You can modify the code on the fly. They may also add extra
RAM, which, at least on the CY7C68013, may be used for either
data or code. But not all of it. Over some portions of the
address space the code and data are separate and some areas
they are not. I have read over the datasheet serveral times,
and at least to me, this is not unambiguously explained.
The only way I was able to get a firm understanding of how
it worked was to write some simple programs to poke values
into memory and read them back. |
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Ian Bell
Guest
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| Posted:
Sat Dec 17, 2005 5:15 pm Post subject:
Re: 8051/2 data and iram memory question |
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Bob wrote:
| Quote: |
Some 8051 derivatives replace the instruction ROM with RAM.
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Do they? Which ones?
Ian |
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Jim Granville
Guest
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| Posted:
Sun Dec 18, 2005 1:15 am Post subject:
Re: 8051/2 data and iram memory question |
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Ian Bell wrote:
| Quote: | Bob wrote:
Some 8051 derivatives replace the instruction ROM with RAM.
Do they? Which ones?
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Examples are the Infineon C868, which boots from EEPROM into RAM, and
targets ROM as the volume device, and a number of '51 USB devices
( TI and Cypress ) load into RAM - they do this, because the RAM is
cheaper than FLASH, in the sizes & process involved, and RAM also
gives a slight speed edge. Again, in this sector the really big
customers can buy MASK devices.
-jg |
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Meindert Sprang
Guest
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| Posted:
Sun Dec 18, 2005 5:15 pm Post subject:
Re: 8051/2 data and iram memory question |
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"Bob" <bob3635x@yahoo.com> wrote in message
news:1134832799.224263.323810@g47g2000cwa.googlegroups.com...
| Quote: | Sorry, maybe I should have spelled out the acronym. I was
assuming that iRAM meant "instruction RAM", but maybe others
were using it as a synonym for "idata" (internal data RAM).
In that light, what you were saying makes a lot more sense
to me now.
|
Ah, now I see your problem too. I am not familiar with the CY type you
mention, it is in fact new to me that derivatives exist with such a type of
ram.
Meindert |
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