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Setting the RESET vector on a 68HC11A0

Hello all,

I am trying to "reverse engineer" some older 68HC11 based equipment. I got a hold of some nice circuit boards with general purpose I/O and since I liked working with 68HC11's some 10 years back I got nostalgic. Only thing is that these are 68HC11A0FN's and therefore without any programmable onboard ROM and there are a couple of things I am trying to figure out since I never dealt with those before.

The board's that I have are using 27C256 EEPROM and a very small serial EPROM that I don't remember the type of (until I get back home from work)

I want to replace the current EEPROM code with my own code but....where do I set the first instruction in the eeprom.

Correct me if I am wrong (It has been a while since i did HC11's): During reset the $FFFE and $FFFF hold the reset vector. But since there is no onbord ROM to program the $FFFE-F must lie on the extrernal EEPROM right??

Will I therefore program the reset vector with something like:

ORG $7FFF ; the last address in the EEPROM JMP $4000 ; Or whereever inside my EEPROM

ORG $4000 ;where the program sets registers and run code. program .....

Is this gonn'a work? Am I on the right track here?????

Any tips and tricks welcom

Thanks,

J=F3n F. Hjartar

Reply to
hjartar
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This is from memory, I do not have any documentation with me and I have not touched a '6811 for years, but anyhow...

I believe the 'A0 has 256 bytes of internal EEPROM, and there is configuration register that allows you to map the location of the interrupt vectors to either external memory or this internal EEPROM.

The chip also had a boot mode where it would configure the serial port to download a small program into internal RAM and then run it, so you can write small test programs to verify the internal EEPROM and config registers without damaging them.

Motorola's data sheets and application notes should provide all the data you need.

Roberto Waltman

[ Please reply to the group, return address is invalid ]
Reply to
Roberto Waltman

No, it should look like: org $7ffe last EPROM word address, $fffe in hc11 map fdb $4000 if your reset code sequence starts at $4000.

(fdb=3D dc.w or whatever, generates 16 bits, MSB first)

Dimiter

Reply to
Didi

You want to have an EPROM programmer that will offset the addresses, otherwise everything will be all messed up, not just your reset vectors. So use

ORG $FFFE ; the reset vector JMP $start ; you really want to use symbolics

then set up the EPROM programmer to offset the start of memory to 8000 hex.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

No, this will produce 3 bytes ($7e ....). He only has to put the address there, no JMP opcode, just as in my previous post.

Dimiter

Reply to
Didi

Whoops -- it's been a while since I've been in the guts of an HC11.

He should still use symbolics.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

Hi,

The correct syntax is :

ORG $FFFE ; the reset vector FDB start

ORG $8000 start: ...

With a 27C256, you only have 32Ko. So, your address decoding must be the negative A15 bit on the /CS pin of the

27C256.

In a 68HC11, if no internal ressource is present at one address, in expanded mode, the external ressource is mapped at this address.

Yvan

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Yvan BOURNE

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