16F877 Programming (newbie)

[Melanie]

>Normal execution of the program thereafter disregards the DATA line??

Yes. The DATA statement simply presets the content of EEPROM at PROGRAM TIME - ie when you burn the PIC in your programmer. The DATA statement is not actually an 'executable' piece of code. It carries no program overhead. It is simply a directive to place values into EEPROM when the PIC is programmed. Thereafter, the content of EEPROM can be read (with the READ command) and altered (with the WRITE command) as often as you want during program execution. So to recap, DATA presets the EEPROM to an initial value at PROGRAM TIME - and at no other time thereafter (unless you reprogram the PIC in your programmer when the value will revert back to that specified by the DATA statement - unless of course you have a clever programmer in which you can specify if the EEPROM contents are to be programmed or not).

>>So is each LOCATION one 8-bit byte long?

Yes.

>>If so, how can you store 16 bit words??

You split the word into highbyte and lowbyte and use two EEPROM locations.

[weirdjim]

Many thanks fer yer help. The derivative of the learning curve is a large positive number today.

Two last questions and I'm pretty sure that I know the answers ... which is generally how I get bit on the hiney from time to time ...

1.) If I am in a particular section of the main program and I call out a subroutine called, for example getthis: and in getthis: it calculates a variable called rxp2 and gives it a value of 7 (i.e. somehow rxp2=7 is generated), when I RETURN to the main program and use rxp2, does it still have the value 7 if it otherwise hasn't been modified? I think the term for this is global variable, where it matters not where in the program something is calculated, it carries that value everywhere in the program until modified somewhere else.

2.) Does it take up any more program space to call a variable s2 or supercalafragialisticexpialidotious2 ??? And are we limited in length on variable names?

(Or is there a place online where I can go to look up information like this rather than bugging you all afternoon?)

Jim

[Melanie]

Actually, where I am now is pretty much midnight...

1. All variables in PICBasic are global.

2. Labels or variable names do not take up program space... make them meaningful, but if you go crazy with them, it makes your program look stupid (but then again, who cares, you're the one that's probably only going to read it and it's unlikely you're going to publish it for a wider audience to riddicule)...

If (PrimaryStallAlarmWarningFlag=1 and PrimaryWheelsUpFlag=1 and WheelsNotDownAndLockedFlag=0) then goto YoureGoingToBendYourPropellerVoiceMessageWarning

Try to make things fit on one line - it makes printouts and debugging so much easier.

With PBP - it's all in the manual and in the Datasheet for the PIC you're using.