[Coco] SCS - $FF40 behavior

[William Astle]

ROM mapping has nothing to do with SCS on the Coco3. If it did, the 
floppy controller wouldn't work under either disk basic or OS9 since 
neither one of those has the ROMs enabled during normal operation.

There is a "SCS" control bit in FF90 that affects SCS, but it has 
nothing to do with ROM mapping. I can't recall if that switches the 
behaviour of the FF4x range or the FF5x range. Most documentation just 
says "Enable standard SCS operation". That bit is set by the stock ROM 
at boot time.

On 2015-10-15 23:04, Chad H wrote:
> What do you mean "only after banking in the ROMs"?  From what I observed on my CoCo 2, a simple PEEK or POKE triggered the SCS line low for a few microseconds then it was released.  Is the CoCo 3 doing something different here?
>
> - Chad H
> http://sites.google.com/site/cbhlab101/
>
>
> -----Original Message-----
> From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of RETRO Innovations
> Sent: Thursday, October 15, 2015 10:19 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] SCS - $FF40 behavior
>
> On 10/15/2015 8:45 PM, Chad H wrote:
>> Well I confirmed the ground triggering of the SCS line by accessing $FF40 is detectable by my o-scope.  Going to mod one of my 512K EEPROM boards and its external Atmega328 driven controller so that the Microcontroller can detect the SCS trigger.  Then going to combine that with a modification to the 25 byte assembly .BIN loader we came up with last year and 'hopefully' allow .BIN loads from EEPROM in excess of 16K by loading it in 8K segments at a time :)  This method, if it works, would keep the EEPROM map area within the &HC000 - &DCFFF 8K space and function for the CoCo 3 as well.   I still don't have a CoCo 3 to verify that $FF40 triggers the SCS line by default on those machines. Any details would be helpful.  If we can load a 512K EEPROM full of .ROMS of any size, and of .BIN's of any size, I think we can remove  most of the downsides people have pointed out.  With the external controller it could be left plugged in and remote bank-switched by the controller to red!
 uce wear o
n the cartridge port.  With larger .BIN file support it could be more useful for these.   Of course, I will have to get re-acquainted with the assembly .BIN loader :/
>>
>> - Chad H
>> http://sites.google.com/site/cbhlab101/
> I can confirm that SCS is low on Coco3 when accessing $ff40, but only after banking in the ROMs.
>
> Jim
>
>
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