Thanks guys,

Most of my frustration is now gone after realizing that at some point I must
have deleted the line that selected bank 0 after setting tris in bank 1. Bit
tests are now reporting as expected.

Why the ^%&^%*^%(&%% doesnt the assembler catch this?  It has those annoying
messages about specifying a bit in bank 1.  Oh well it is free.

We you are a newbie like me it is very easy to completely blow the mind and
requestion everything that you think you understand.


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jinx
Sent: Tuesday, May 21, 2002 4:05 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC] - Detecting the press of a button


(after carefully checking there's no SPDT in sight)

> Can someone please give me a small checklist of what
> it takes to detect the press of a button? Include setup of
> port, pullup conditions,wiring, bit testing, etc.

Bank1 - set trisb bit4 to 1 for input

Test PortB,4 in Bank0 - even banks are port, odd banks are tris

Pulldown to Vss, pushbutton to Vcc or pullup to Vcc, pushbutton to Vss

Wires as short as possible, add a buffer/driver for over,
say, 1m but that may depend on the value of the resistor,
quality of wire, environmental noise etc. Adding an RC
network will help filter any noise from the pushbutton. Put
a high (compared to the R, eg R=10k, discharge=100k)
value resistor across the C to discharge it after the push-
button is released

> btfsc PORTB,4
> call rb4on
> return

should be OK for checking the default state if using a pulldown

With a pullup and grounded pushbutton you'd change the test
for default to btfss

If you've just the one pushbutton you might consider RB0/INT

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