Hi,

On top of what Roman Black has said, are you using the data latch facility
of the 4511?

Put the data onto the bus and then pulse pin 5 low to latch the data to the
decoder. After that, so long as pin 5 is high, you should be able to read
the bus without upsetting the display.

Philip Martin.


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Roman Black
Sent: 10 March 2001 13:05
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]:


Joe Denehan wrote:
>
> I'm building a circuit that reads from the BCD input of a 7-segment
decoder.
> I'm using LE as the trigger to the PIC16F84 to capture the BCD code.
Problem
> is when I connect to the input of the BCD chip 4511 the 7-segment display
> flickers and displays wrong digits, I tried using a opto-isolator and an
> Op-amp 741( as Unity Gain Follower) but the display I'm reading from is
> still affected by branching the trigger to my circuit, circuit works OK on
> breadboard with clock for trigger. Anyone any ideas?


Yes, you are obviously loading the inputs to
the 4511. Being cmos logic, whatever drives them
should be ok to drive 10 or more cmos inputs.

The only sensible guess would be that you have
not configured the PIC inputs properly, and you
are connecting PIC outputs to the 4511.
Check your code that sets the tristate in/out
settings for the PIC pins you are using, and
especially check the bank switching for the PIC
chip, on some chips the TRISB etc are on the
same bank as the PORTB, other PIC chips you have
to change banks to do the tristate.
-Roman

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http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.