[Coco] Disto 512k upgrade board

[Arthur Flexser]

Kip, I'm reasonably sure that this strange behavior isn't due to any
inaccuracies in  the floating point-to-hex conversion routines.

There were changes made to the Color Basic startup sequence for the
CoCo 3, and I strongly suspect that the code at $A074 in a CoCo 3 is
not what you're looking at in the Unraveled book.  I suspect you're
doing something like jumping into the middle of an instruction and
knocking a hole into the floating point evaluation routines.  Also,
Super Extended Basic may be further patching into the code around
there.  Try disassembling what is at $A074, and I think you'll find it
is not what you were expecting.

Art

On Fri, Dec 13, 2013 at 5:29 AM, Kip Koon <computerdoc at sc.rr.com> wrote:
> Hi All!
> I looked in the Color Basic Unraveled book in the Disassembled Listing for
> the WARM START FLAG detection sequence at the beginning of the code and upon
> detecting no warm start flag, control is transferred to BACDST or the Basic
> Cold Start routine which is $A074, so I typed in a simple one command
> statement using &H to precede the hexadecimal number A074 like this
> EXEC &HA074
> to see if the code would Cold Start DECB 2.1 on the Coco 3.  I tried it in
> VCC to make sure it would work and it did.  Then I thought, what about those
> individuals that prefer all decimal numbers, so I converted $A074 to 41076
> and tried it expecting that to work also.  I typed in
> EXEC 41076
> and guess what?  It didn't work!  VCC Coco 3 got lost!  I thought that was
> very strange.  I tried it on a real Coco 3 and it didn't work there either.
>
> Then I got to thinking.  Could it be true that since &HA074 is already
> hexadecimal, the Basic Interpreter may just be directly using that number as
> an execution address?  Could it also be true that since 41076 is decimal and
> since Basic needs to convert that to a hexadecimal number to be able to use
> it as a memory address to transfer control to, somehow during the conversion
> process of changing 41076 decimal to $A074 Hexidecimal that a conversion
> error took place and the end result is not exactly $A074?  I would imagine
> the floating point routine is not exactly perfect.
> Years ago back in the early 1980s, I wrote a BASIC program on the Altair
> 8800B running a Microsoft Time Sharing Basic Interpreter computer system
> there in the computer room in the Electronics Engineering Technology Wing of
> Spartanburg Technical College to convert Decimal numbers to and from
> Hexidecimal and Binary.  "0.1" turned out to be a repeating binary number
> according to the conversion process I learn back then.
> Though I don't exactly know how Color Basic is converting a decimal number
> to a hexadecimal number for the EXEC command, I'm thinking something is
> wrong with the math routines.  Can anyone who understands the math routines
> implemented in 6809 assembler code better than me check to see if this is
> true?  It would be interesting to see if there are any other errors in the
> math routines.
> So, I guess I'm relegated back to the
> POKE 113,0
> and pressing the <RESET> button to cold start my little Cocos.  At least
> that will work on any Coco, a 1, 2 or 3.  Take care my friends.  Qaplah!
> Starfleet Out!
> Kip
>
> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On
> Behalf Of William Astle
> Sent: Thursday, December 12, 2013 3:30 PM
> To: coco at maltedmedia.com
> Subject: Re: [Coco] Disto 512k upgrade board
>
> On 13-12-12 01:10 PM, Mark Marlette wrote:
>> No 20 count......
>>
>> POKE 113,0:POKE 49152,0:EXEC40999
>>
>
> How does zeroing out the first byte of the DECB range help anything? All
> that'll do is stop extended basic from initializing DECB.
>
> For a proper cold start, better to EXEC&H8C1B (35867) on a coco3 - that will
> actually trigger the internal boot rom. 40999 (A027) does not.
> Triggering the internal rom will recopy the ROMs to RAM which may be helpful
> if you messed something up.
>
>
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