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From: mfogarty@netcom.com (Michael Fogarty)
Subject: Re: Booting 68HC11 from EEPROM?
Message-ID: <mfogartyCLotML.Bv1@netcom.com>
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References: <GAS.94Feb23094111@globus.ffi.no>
Date: Wed, 23 Feb 1994 17:23:08 GMT
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Geir Atle Storhaug (gas@globus.ffi.no) wrote:
: Is it possible to boot the 68HC11 (in singlechip mode) from the onchip EEPROM?
: This could be interesting for small applications (< 256/512 bytes).

Yes it is.  Check the HC11 pink book (M68HC11RM/AD REV 3):
Page 3-17:

Section 3.5.4.4 BOOTLOADER FIRMWARE OPTIONS
...If a break character is received at this point, instead of the $FF,
an immediate jump to the start of EEPROM ($B600) is executed.  Since
the bootloader already transmits a break character, the user can tie
the RxD and TxD pins together and to a pullup resistor, and then reset
the part in special bootstrap mode.

This procedure will cause a direct jump to EEPROM at $B600.  Tying the
RxD line low will not accomplish the same result because a high-to-low
transition is required to indicate the beginning of a start bit ...
----------------------------------
NOTE 1:
Special bootstrap mode is set by grounding the MODA and MODB pins and
doing a reset.
NOTE 2:
Don't do as someone else on the net has recently done (I can't remember
where I read this).  He tied the TxD and RxD lines of his MAX232 TTL->RS-232 
converter together.  The processor wasn't interested.  You must connect
these pins at the processor.

Mike
