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RE: [avr-gcc-list] Difficulties switching from Mega103 to Mega128

From: Scott and Roxanne Munns
Subject: RE: [avr-gcc-list] Difficulties switching from Mega103 to Mega128
Date: Tue, 12 Aug 2003 20:04:43 -0500


Are you using PORTA and PORTC as I/O ports or as address/data ports to
memory-map the VFD into the Mega128's data space?  Some of your previous
comments hinted one way, and some hinted the other way, so I'm not sure.  If
you don't know, check for a 74x573 latch (or equivalent) between the PORTA
lines and the VFD.  If you have one, it's probably using the external memory
interface (memory mapping).  You can also check in the software to see if
the MCUCR register has the SRE bit (bit 7) set.  If so, the external memory
interface is enabled.

It appears that my colleague may have solved the problem between the Mega103
and the Mega128 in Mega103 compatibility mode today.  The timing and
presentation of address and data info on the external memory interface has
definitely changed (try comparing timing diagrams of both processors).  It
seems that inserting a "nop" in between any consecutive reads and writes
through the external memory interface "solves" the problem.  Since the code
was written in assembly, it was easy to find and change the behavior.  As we
learn more about the exact failure mode and whether this is an Atmel issue,
LCD display driver issue, or just a bad combination of the two, I'll post
updates to the list.


-----Original Message-----
From: Brian Korsedal [mailto:address@hidden
Sent: Tuesday, August 12, 2003 12:39 PM
To: address@hidden
Subject: RE: [avr-gcc-list] Difficulties switching from Mega103 to


We have a VFD connected to the PORTA and PORTC.  I inherited the project, so
I'm not sure exactly how we use these ports, I'm learning it now.  I was
wondering if you solved your problem with the external memory interface?  We
are using the same pins and might have the same problem as you are having.



-----Original Message-----
From:   Scott and Roxanne Munns [mailto:address@hidden
Sent:   Wed 8/6/2003 7:03 PM
To:     address@hidden
Subject:        [avr-gcc-list] Difficulties switching from Mega103 to Mega128
Greetings everyone,

My group at work is currently involved in converting an LCD/touchpad
controller board from the Mega103 to the Mega128.  We fully expected to be
able to drop in the new part, put the Mega128 in Mega103 compatibility mode,
and have the old software work just fine.  However, we haven't been so
fortunate.  The display shows corruption of most of the bitmaps placed on
the screen - it looks very "smudged".  The pattern isn't a fixed offset, and
it changes from time to time.

The hardware design uses the external memory interface to "memory map" the
display driver - only 2 bytes of address space used for the interface.
Preliminary analysis appears (maybe) to point at a change in the timing of
the external memory interface between the Mega128 and Mega103.

Has anyone run into similar problems?  Any suggestions, solutions, or things
to check into?

Thanks for your help (and sorry for being off-topic),
Scott Munns

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