[Coco] DLOAD

[Arthur Flexser]

Roger, I seem to recall that on the CoCo 3, DLOAD is overwritten in the ROM code
as well, with a jump to the reset vector or its equivalent somewhere in the
early part of the routine.  I think they left most of the code intact but
patched in the reset. Not 100% sure, though.  If that's the case, you should be
able to restore the original code in RAM and use it.

Art

On Tue, 21 Mar 2006, Roger Taylor wrote:

> 
> I'm trying to figure out if it's possible to enable the DLOAD comnmand on 
> the CoCo 3.  I realize that the ROMs are running from "All-RAM" mode and 
> that DLOAD is normally overwritten, but when I switch to ROM mode (POKE 
> 65502,0) DLOAD still does a warm boot or reset.
> 
> Has anybody experimented with this?  I'm going to dig into the ROM source 
> tonight and see what's happening.
> 
> Also, I've tried DLOAD on two CoCo 2's and neither one will send out over 
> the bitbanger port correctly at the 1200bps setting.  300bps works 
> great.  Using a serial port monitor on the PC, it shows that no matter what 
> cable I use and CoCo I use, sometimes the byte (138) gets received as (10) 
> on 2 different PCs, which tells me that there is probably a bug with the 
> 1200bps setting which is small enough that a start bit and 7 data bits 
> makes it ok into the PC but the 8th data bit isn't stable.
> 
> Using two PCs (one with a standard COM port and the other with a 
> USB-to-serial adaptor), two CoCos, two cables, no matter how I mix and 
> match them, I get the same results trying to use DLOAD "FILE",1  the 
> 1200bps setting.
> 
> So, my tests prove that it's the delay value for 1200bps in the DLOAD 
> command.  The code (or the Unravalled Series PDF files) shows that the 
> delay for 300bps is 44 and the delay for 1200bps is 44*4, but since the 
> BASIC printer output code doesn't use constant-scaled delays, I can't see 
> why DLOAD can.
> 
> The only way I can test this theory is by using a 64k CoCo 2 which has been 
> put into the All-RAM mode where the ROMs are copied into RAM and run from 
> there, and I can patch the DLOAD code.
> 
> 
> 
> 
> -- 
> Roger Taylor
> 
> 
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