68300

Charly,
 
The port E and port F pins do not have pull-ups or pull-downs.  When these ports are configured as I/O by pulling D8 or D9 low at the release of reset, the Port E and F pins just more or less do what they want to do.
 
Depending upon which wafer line the parts are manufactured in, the 68300 devices will sort of float high (very weak internal pull up that you can't always depend on).
 
The bottom line is this:  If you need a Port E or a Port F pin to be at a definite state when configured as an input, it is up to you to make sure that the pin is appropriately tied to something.  If the pin floats (when configured as an input) you will not be guaranteed of anything.
 
It is my experience that if you let the DSACK pins float, they will eventually float low and give  an incorrect termination to a bus cycle, i.e., an 8-bit dsack may get signaled by the external DSACK pins instead of what ever the internal CS option register is programmed to.
 
Also, don't get fooled by looking at floating port E and F pins and getting the impression that they really do get pulled up.  The "pull up" is from very weak devices and leakage plays a very important aspect here.  Does anyone want to depend on "leakage currents.
 
Anyway, keep in touch,
 
Regards,
 
Charlie

-----Original Message-----
From: Charly Mauron [mailto:charly.mauron@...]
Sent: Tuesday, August 13, 2002 10:34 AM
To: 68300@yahoogroups.com
Subject: [68300] SIM I/O pins


Hello !

I'm working with  the CPU32.

Are the SIM I/O pins of the Port E and F internal pulled up (or down) ?

Thanks for the answer.

Charly


_____________________________

Charly Mauron
R & D Monitoring Systems

charly.mauron@...
Direct Phone : ++41 (41) 766 43 17
Fax : ++41 (41) 761 08 80

SCHILLER AG Switzerland
Altgasse 68
CH-6341 Baar
www.schiller.ch
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