[Coco] coco1 64K extended basic SN ERROR

[Charlie Pelosi]

Thanks for the reply, Robert.
Indeed both of my 64K coco1 do the same thing. My 64k coco2 does not. Not a 
big deal to just type RUN again, was simply curious.
Thanks again!

Charlie


--------------------------------------------------
From: "Robert Gault" <robert.gault at att.net>
Sent: Friday, September 05, 2014 11:16 AM
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Subject: Re: [Coco] coco1 64K extended basic SN ERROR

> Charlie Pelosi wrote:
>> I have a 64K coco1 with Extended Color Basic. With some basic programs it 
>> gives me a ?SN ERROR but if I simply type RUN again the program runs fine 
>> with no error.
>>
>> One example is the game BUGS found here: 
>> http://www.colorcomputerarchive.com/coco/Disks/Games/Bugs%20(Color%20Computer%20Magazine).zip
>> When I run BUGS.BAS it says ?SN ERROR. (no "in line number", just ?SN 
>> ERROR) I type RUN again and the game runs fine. Some experimenting tells 
>> me it never gets past the 1st line of the program.
>>
>> 0 CLS0:PCLEAR1:FILES0:CLEAR5,5119:GOTO4
>>
>> Another example is Jim Gerrie's Dungeon Crawl.
>> http://rsp.retrocomputacion.com/games-jim-gerrie-ports-4-of-his-games-to-the-tandy-coco/
>> When I RUN"CRAWL I get ?SN ERROR IN 0
>> Entering RUN again and the game runs without the error.
>> Line 0 reads:
>> 0 
>> PCLEAR1:GOSUB2600:CLEAR1300:DIMA$(15),B$(15),C$(15),D$(24),E$(24),I$(27),D(20,20,2),W$(34):GOTO900
>>
>> Now, I know the coco3 does not have this issue. Not sure about BUGS but I 
>> know Dungeon Crawl starts on the 1st RUN.
>> What is the issue with the coco1? I will drag out my coco2 and try with 
>> that. Perhaps this is a known issue with ECB?
>>
>> Charlie
>>
>>
>>
>>
>>
>
> There is a PCLEAR bug in early versions of Extended Basic. Bugs and Crawl 
> will RUN the first time if you manually enter a PCLEAR1 before starting 
> the program.
>
> If you want to understand the bug, you will need to study the "Unravelled" 
> series at $96A3.
>
> The workaround used by Coco1 programmers was to have
> 0 GOTO1000            or whatever would be the last line in the program
> 1000 PCLEAR1:GOTO 10  or whatever the "first" actual line would be
>
> Since the programs in question already use a line 0, they would need to be 
> renumbered with the RENUM command to use the above.
>
> Robert
>
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