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Re: 8051/2 data and iram memory question



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The Intel 8051 Always had IRAM It was just a different way to address the RAM.
Indirect as opposed to direct. MOV as opposed MOV @R0



Re: 8051/2 data and iram memory question
In comp.arch.embedded,
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IRAM = internal RAM, not instruction RAM

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Yes, that datasheet will help.

In 8051 terms, IRAM is a completely seperated dataspace. One part of this
space is bit-, direct- and inderect-adressable, one part direct and indirect
and one part only indirect.

This IRAM space was 128 bytes on the original IIRC and newer parts may
have up to 256 bytes.

Then there is external RAM, XRAM, which is maximum 64kB (without paging) the
address space is completely seperated from the IRAM and you even need
different instructions to access it.

To add to the confusion, newer parts sometimes have XRAM on-chip. So you
could call that internal external RAM :-(.

The Atmel AT89C51AC2 (for example) has 256 bytes IRAM and 1kB XRAM on-chip
If you add external XRAM in the bottom of the address space, the bottom 1kB
of the external RAM will not be used. So if you add a 32kB chip there, you
will end up with 32kB of usable XRAM, not 33kB.


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