[Coco] "Reading" non-readable bytes with PEEK vs ZBUG

[Robert Gault]

Roger Taylor wrote:
> At 07:31 AM 1/26/2008, you wrote:
> 
>> Roger Taylor wrote:
>>
>>> At 07:38 AM 1/25/2008, you wrote:
>>>
>>>> There is another approach which will be independent of memory but 
>>>> not relocated DOS code. Write a Basic program as a LOADM routine for 
>>>> your binary program.
>>>> 10 A=PEEK(&HC003)
>>>> 20 IF A=8 THEN POKE&HD008,&H21 ELSE POKE&HCF2C,&H21
>>>> 30 LOADM"ROGER.BIN"
>>>
>>>
>>> I now see that you're checking a byte first.  I didn't notice that 
>>> earlier, sorry.
>>
>>
>> Also I goofed when writing this short piece of code. I intended a BRA 
>> to replace the BEQ but used the value for BRN, duh.
>>
>> The POKE value should be &H20 to get the BRA.
> 
> 
> 
> Robert,
> 
> What is the other ROM version you're patching?  DECB 2.1 looks like the 
> A=8 condition, for sure.
> 
> 

Right, line 20 should read
20 IF A=8 THEN POKE &HD008, &H20 ELSE POKE &HCF2C, &H20

That will be for DOS1.1 A=8 and DOS1.0 A=4. Far as I know this test will 
work with other third party DOS but you should check with Art about his 
software. What is important is that the BEQ verification test is at the 
indicated locations. Oh, and don't worry about the DECB2.x as the 2 just 
means Coco3 not a change in DOS.

RGBDOS and therefore HDBDOS should also be covered.