Hello,
> I'm using GPBUS to read/write a number of 8-bit ports. My problem is
> reading using GPBUS read cycle doesn't seem to work. Writing a port
> works flawlessly, but with a read cycle, GPBUS pins 0-7 remain as
> outputs and that drives my card's outputs to the programmed data value
> for those bits, which I'm not sure what should be.
You are correct during a read cycle the GPBUS pins 0-7 should be
tri-stated. I tested this and couldn't reproduce the problem... I
configured DIO 0-10 as outputs.
$ poke8 0x12c00000 0xff
$ peek8 0x12c00001
0x40
$ poke8 0x12c00001 0x47
Next I drove DIO_0-DIO_7 low and connected a pullup to 3.3V on DIO_0-DIO_7.
$ poke8 0x12c00002 0x00
I found when I did a read of the GPBUS, DIO_0-DIO_7 pulled high.
$ peek8 0x60c00000
This implies DIO_0-DIO_7 were tri-stated during the read...
> 7400's info doesn't
> specify if data bits should be 0xff or 0x00 in order to accomplish a
> read.
The state of DIO_0-DIO_7 during a read are don't cares as they should be
tri-stated.
Contact me off list if you'd like an RMA to return your board...
--
Best Regards,
______________________________________________________________
Eddie Dawydiuk, Technologic Systems | voice: (480) 837-5200
16610 East Laser Drive Suite 10 | fax: (480) 837-5300
Fountain Hills, AZ 85268 | web: www.embeddedARM.com
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ts-7000/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/ts-7000/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
|