Re: CHRGET, how does it work?

From: didier derny <didier_at_aida.org>
Date: Thu, 26 Oct 2017 11:26:25 +0200
Message-ID: <594853ae-4b7c-d43f-b4b6-184841998010@aida.org>
yes the the charget is modified from the rom  (a pointer is updated)

so some part of the charget  must be left intact (the part where the 
pointer is located)

it is widely used by jsr $BD98  on the commodore 8000

all extension to basic hack this function to intercept the new commands...


I used it the eighties for my own extension but  I dont remember very 
well the details...



Le 26/10/2017 à 11:20, Anders Carlsson a écrit :
> Ruud Baltissen wrote:
>
>> lda $EA60 ; get byte to scan, address set by call routine
>
>> The problem I have is the instruction "lda $EA60". Lee's comment says 
>> that $EA60 stands for RTS/NOP but I take that with some grains of salt.
>
> Forgive me if I'm barking up the wrong tree, but isn't the entire 
> CHRGET routine in zeropage RAM, which means it keeps modifying itself 
> all the time? Thus the $EA60 would be a placeholder in ROM before 
> copying the routine to RAM and you would want to look for a routine 
> that modifies the ZP as the program is interpreted.
>
> Best regards
>
> Anders Carlsson
>
>
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Received on 2017-10-26 10:00:55

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