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From: zimmer@calvin.tmc.edu (Andrew Zimmerman)
Newsgroups: sci.electronics
Subject: Re: MC68705 stack question
Message-ID: <1025@helens.Stanford.EDU>
Date: 14 Sep 90 10:40:54 GMT
References: <1990Sep12.145331.6233@jts.com>
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Reply-To: zimmer@calvin.UUCP (Andrew Zimmerman)
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In article <1990Sep12.145331.6233@jts.com> gil@jts.com (gil) writes:
>
>I am currently working with the Motorola 68705 uP and have noticed the
>absence of stack operation instructions (push/pop etc.).
>
>Does anyone have any ideas about gaining access to the stack pointer,
>i.e. is it shadowed in RAM somewhere or are there any undocumented
>op-codes to do this?
>
>+-----------------------------+-------------------------------------------+
>| Gil Hauer, Tech Noir Inc.   |       gil@jtsv16.jts.com                  |
>| Toronto +1 416 653-8276     |  or:  uunet!jtsv16!gil                    |
>+-----------------------------+-------------------------------------------+


     This is going to be a gross hack, you might not want to read any
further.  The only way that I can see to do this is to have a subroutine
that you call, and then set the x register to ff and move back through
the stack looking for the address of the called subroutine.  This might not
work if the CC's can be set such that they could be the same as the 
subroutine address, I haven't checked into that yet.  
     I am having the exact same problem in writing a small monitor for the
68h805.  Okay, I'm not writing the monitor, I'm stealing parts of the
monitor fro the 05 and the evaluation version of the 805PA1.  Currently,
my version of the monitor has the Dump, load, Go, and the Bulk erase 
command.  I am currently adding the register commands.  The monitor takes
up the B-array, and the bulk erase only erases the A-array.  If anyone
wants what I have, I will make it available via anon-ftp.  


Does anyone know if the Vpp charge pump bit has to be set on the
prototype version of the 805 which needs 19.75 volts?  For those who need
this voltage, the TL497 works great.  Using that chip and the MAX232, all 
you need is +5 and Gnd.  

Andrew
zimmer@calvin.stanford.edu

PS.  I wish all companies had the same customer relationship that 
Motorola has.  They are extremely helpful.