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mikewm
 Post subject: MSBASIC on a 6502 SBC
PostPosted: Fri Feb 23, 2024 10:20 pm 
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Posts: 2
I've fabricated a 6502 SBC based on the Ben Eater videos. My board integrates four LED's on PIA PORTA bits 0-3. I've got MSBasic running as Ben demonstrated in his last video. I've added some assembly routines to the Wozmon monitor to control the 2x16 LCD and the LED's.

I ran into an unexpected hitch when when writing a BASIC program to control the LED's. Here's the output from the serial interface:

Code:
OK
1 DDRB = 32770
2 DDRA = 32771
3 PORTB = 32768
4 PORTA = 32771
5 LCDTRIGGER = 47
RUN

?SYNTAX ERROR IN  3
OK
POR = 4

?SYNTAX ERROR
OK
PO = 4

OK
POB=4

OK


The SYNTAX ERROR occurs both in the program and when entered directly anytime I try to assign "POR" or "PORxxxx" to a number. It seems that "POR" and derivatives starting with "POR" are reserved for some reason in MSBasic.

Has anyone seen this that can explain what's going on.
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drogon
PostPosted: Fri Feb 23, 2024 10:39 pm 
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Joined: Wed Feb 14, 2018 2:33 pm
Posts: 1398
Location: Scotland
mikewm wrote:
The SYNTAX ERROR occurs both in the program and when entered directly anytime I try to assign "POR" or "PORxxxx" to a number. It seems that "POR" and derivatives starting with "POR" are reserved for some reason in MSBasic.

Has anyone seen this that can explain what's going on.


One thing to note is that MS basic only uses the FIRST 2 letters of a variable name, so PORTA is the same as PORTB.

The reason you're getting an error is due to PORTB having the OR keyword inside it. It's interpreted as P OR TB which is a syntax error on the left side of the = sign...


Try just DA, DB, PA, PB and so on.

-Gordon

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Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/
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mikewm
PostPosted: Sat Feb 24, 2024 3:08 am 
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Posts: 2
Thanks Gordon!
Code:
OK
1 PDDRB = 32770
2 PDDRA = 32771
3 PRTB = 32768
4 PRTA = 32769
5 LCDTRIGGER = 47
6 REM
10 PRINT PDDRB, PDDRA
20 PRINT PRTB, PRTA
30 END
RUN
 32771          32771
 32769          32769

OK


Interestingly, the code above worked without generating the SYNTAX ERROR. However, the variables sharing the common first two letters took on the latter of the assignments.

It's been a long time since I've programmed in Basic, as in early '80s on an Apple II. I wonder if Applesoft Basic had the same restriction and I just forgot. Will need to check on that.
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barrym95838
PostPosted: Sat Feb 24, 2024 4:16 am 
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barnacle
PostPosted: Sat Feb 24, 2024 6:18 am 
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Posts: 660
Location: Potsdam, DE
The classic BASIC confusion I was taught many many years ago was 'FORD=STOP' which does _not_ copy from one variable to another :mrgreen:

Neil
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Yuri
PostPosted: Sat Feb 24, 2024 7:11 am 
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Goes to show how very loose the BASIC parser was compared to more modern languages.
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drogon
PostPosted: Sat Feb 24, 2024 8:16 am 
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mikewm wrote:
It's been a long time since I've programmed in Basic, as in early '80s on an Apple II. I wonder if Applesoft Basic had the same restriction and I just forgot. Will need to check on that.


All 8-bit MS Basics are like that. Just use 2 character variable names.

-Gordon

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Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/
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