16F877 vs. 16F877A

[Melanie]

If you compare the Datasheets you'll discover the 877A has Comparators and a Voltage Reference module which can bite you if not disabled.

[DavyJones]

If you compare the Datasheets you'll discover the 877A has Comparators and a Voltage Reference module which can bite you if not disabled.

Melanie, Thanks

To shut them down correct?

adcon1=7 
cmcon=7

By chance can you tell me the page/section that is in that discusses it? I just searched through my data sheet and I don't see anything specific to the 877A. I am obviously missing it.

thanks for your time
David

[DavyJones]

adcon1=7 is essentially the same as ADCON1 = 1110 right? I am not a complete loser am I?

[Bruce]

Normally you'll want to set HS_OSC for any crystal frequency over 4MHz. Some 4MHz
crystals may work with the higher drive levels, some won't.

With HS_OSC OSC2 provides a higher drive level to the crystal. With XT it's lower. The
lower drive level with your 10MHz crystal was most likely not providing enough for the
crystal to start up.

Here's an excellent set of basic PIC training modules: http://techtrain.microchip.com/x14/

Download & go through the one on oscillators.

adcon1=7 is essentially the same as ADCON1 = 1110 right?

Nope. ADCON1 = 7 is the same as ADCON1 = %00000111, which makes all analog pins
digital.

ADCON1 = %00001110 is the same as ADCON1 = 14, which leaves AN0 set to analog, and
the rest digital.

[Melanie]

I just searched through my data sheet and I don't see anything specific to the 877A.

Huh? I thought the PIC16F877A Datasheet is ENTIRELY DEVOTED to the PIC16F877A!!!

Look at the section on Comparators (section 12), look at the Voltage Reference Module (section 13).

Datasheet=Dowloaded from Microchip
Datasheet 877A < > Datasheet 877
Datasheet < > PBP Manual

adcon1=7 is essentially the same as ADCON1 = 1110 right?

Ugh.... no.

adcon1=7 is the same as ADCON1=%00000111... note the % in the statement specified BINARY, whilst the absence of anything implies DECIMAL.

ADCON1=1110 is the same as ADCON1=%10001010110... now you might find that the ADCON1 register just doesn't have that many bits...

I am not a complete loser am I?

I don't know you well enough to validate that statement! But hey, we've all been there sometime.

[DavyJones]

Huh? I thought the PIC16F877A Datasheet is ENTIRELY DEVOTED to the PIC16F877A!!!

You are correct they look so similiar I am so used to looking at just the 16f877 same thing happened when I was ordering too.

Ugh.... no.

adcon1=7 is the same as ADCON1=%00000111... note the % in the statement specified BINARY, whilst the absence of anything implies DECIMAL.

ADCON1=1110 is the same as ADCON1=%10001010110... now you might find that the ADCON1 register just doesn't have that many bits...

Again my lack of posting correctly. I meant to say
ADCON1=%000001110
I abbreviated that I was trying to imply a decimal value of 111 my mistake I should have been more concise.

I want to use RA0 as my analog in thats not a problem with the 877A is it?

[Melanie]

Stop messing with ADCON1. If it worked for the 877 it'll work for the 'A'.

Just deal with CMCON and CVRCON.

[mister_e]

You might have some issue with winpic software. If I remember correctly, there's a slight difference in the programming between 16F877 and 16F877A.

Make sure winpic support the A version or you select it before programming your PIC, and try to do a programming check.

[DavyJones]

Stop messing with ADCON1. If it worked for the 877 it'll work for the 'A'.

Just deal with CMCON and CVRCON.

Will do I just wanted to double check myself making sure I had that set correctly which it's apparent I do.

By default it looks like according to the 16F877A (I just downloaded the correct data sheet) that CVCRON by default is off so I need'nt worry about that correct?

You might have some issue with winpic software. If I remember correctly, there's a slight difference in the programming between 16F877 and 16F877A.

Make sure winpic support the A version or you select it before programming your PIC, and try to do a programming check.

I checked to make sure both microstudio and winpic have the 877A listed and made sure they were selected when I compiled and uploaded. FYI. WinPic auto detected the 877A and set itself.

Thanks all

David

[Byte_Butcher]

adcon1=7 is essentially the same as ADCON1 = 1110 right? I am not a complete loser am I?

Errr..... ADCON1 = 1110 looks more like 14 to me.

How about ADCON1 = 0111

[Byte_Butcher]

Errr..... ADCON1 = 1110 looks more like 14 to me.

How about ADCON1 = 0111

Sigh... forgot my $...

How about ADCON1 = $0111

Dang, I sure wish the "edit post" button would come back....




steve

[Melanie]

$0111 = 273 = %100010001

Go into your OS Accessories Folder, call up the CALCULATOR, set the view into SCIENTIFIC MODE - it might help.

I'll get back to everyone on the Forum Editing bit.