68HC11 port B

[john]

Hi,

I am having problems with the port B. Its an output port and I am
writing the whole port. My code is as follows

ORG 2000
LDAA $# FF
STAA $1004

Now, if I write 00 hex or FF to theport. The port is always floating.
I tried pull ups and pull downs but no difference. Please advice.
Thanks

Regards
John

 

[Tim Wescott]

Hi,

I am having problems with the port B. Its an output port and I am
writing the whole port. My code is as follows

ORG 2000
LDAA $# FF
STAA $1004

Now, if I write 00 hex or FF to theport. The port is always floating.
I tried pull ups and pull downs but no difference. Please advice.
Thanks

Regards
John

The 68HC11 that I worked with allowed you to program the direction of
the port -- with the direction bit flipped one way (0 IIRC) the port was
a high-impedance input, and with the direction bit flipped the other the
port was an output. Most of those ports could also be configured for
open-drain output, if you so desired.

 

[James Beck]

The 68HC11 that I worked with allowed you to program the direction of
the port -- with the direction bit flipped one way (0 IIRC) the port was
a high-impedance input, and with the direction bit flipped the other the
port was an output. Most of those ports could also be configured for
open-drain output, if you so desired.

Not PORTB.

 

[Rich Grise]

I am having problems with the port B. Its an output port and I am
writing the whole port. My code is as follows

ORG 2000
LDAA $# FF
STAA $1004

Now, if I write 00 hex or FF to theport. The port is always floating.
I tried pull ups and pull downs but no difference. Please advice.
Thanks

Take a look at the data sheet, and look for the "Data Direction Register",
or DDR. You'll need to configure the port as "output".

In case you're trying to do this without a data sheet, here's one:
http://www.freescale.com/files/microcontrollers/doc/data_sheet/M68HC11E.pdf

Also, are you trying to run it in expanded or special test modes?

Good Luck!
Rich

 

[James Beck]

Take a look at the data sheet, and look for the "Data Direction Register",
or DDR. You'll need to configure the port as "output".

PORTB is not bidirectional and has no DDR.

 

[Rich Grise]

PORTB is not bidirectional and has no DDR.

So, the OP is Simply Out of Luck. )-;

Thanks,
Rich

 

[James Beck]

So, the OP is Simply Out of Luck. )-;

Thanks,
Rich

Well, yes and no.
He wants to treat it like an output, so I guess it is fortunate that
PORTB is an output only port, but if it is truly "floating" then he is
screwed.

 

[bruce varley]

PORTB is not bidirectional and has no DDR.

And in expanded mode it outputs low order address bits. Could that be your
problem?