17 Aug
2008
17 Aug
'08
12:27 p.m.
Scanning wrote:
Philip,
Could you execute a small loop in RAM that iterates the flash and pukes the
code byte by byte onto the serial bus ?
No -- the 8051 latches the state of the EA (External Access Enable) pin on
startup. This is the pin that tells the chip whether to run from internal ROM
or from an external ROM.
If it's running from ext-ROM, the MOVC instruction won't work (or it'll read
from ext-ROM).
It's also a Harvard architecture MCU, so the code and data spaces are
separate. You can't just JMP MY_EVIL_ROUTINE_IN_RAM and dump the ROM that way.
Princeton (Von Neumann) architecture chips like the 8086 will allow this, and
the 8051 will if you wire-OR /PSEN with /RD. It's not really a common
configuration though, and only works when the 8051 is being operated as an
external CPU.
Thanks,
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/