-----------------------------------------------------------------------------
THIS FILE: ftp://cher.media.mit.edu/pub/projects/miniboard/hobbytip/11a1boot.txt
CREATED:   Wed Feb 23 1994
MODIFIED:  Tue Feb  6 10:53:38 1996
-----------------------------------------------------------------------------

Article: 8531 of comp.robotics
Newsgroups: comp.robotics
From: mfogarty@netcom.com (Michael Fogarty)
Subject: Re: Booting 68HC11 from EEPROM?
Date: Wed, 23 Feb 1994 17:23:08 GMT
Lines: 28

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


Date: Tue, 6 Feb 1996 16:04:21 +0100
To: robot-board@cmf.nrl.navy.mil
From: artelse@media-gn.nl (J.Arthur Elsenaar)
Subject: Re: How to use 68HC11 A1 version in single chip mode?
Sender: owner-robot-board@cmf.nrl.navy.mil
Precedence: bulk

At 08:47 06/02/96, Clay Timmons wrote:

>I know that you can tie TX and RX together to cause
>a jump to EEPROM ($B600) after reset but I cannot
>do this since I need TX and RX for serial communication.
>
>
>Any ideas?

Recently I read a quite smart solution to this. What the designer did, was
to add some cmos swithes (4066/4016) to the TX/RX lines to tie them
together only at reset for a short amount of time (RC delay).

Haven't got the mag at hand, but hopefully it directs you somewhat.
If you really want more details, mail me.

regards Arthur.

___________________________________________________________________
J.Arthur Elsenaar.               Tel+Fax: +31-50-3136467
artelse@media-gn.nl
___________________________________________________________________