[Coco] Access to 225 lines in BASIC

[Bill Pierce]

Nick, I think (IMHO), that they kept the 192 due to the 8x8 font matrix for text characters. To go to the full resolution left extra "unused" lines, even if they went to an 8x7 or 7x7 (6x7?) font. They ran into the same problem when rewriting the screen drivers for NitrOS9. NitrOS9 allows you to setup the screen for the extra lines but it's always a little "off". It also made the math easier :-)
 

Bill Pierce
"Today is a good day... I woke up" - Ritchie Havens
 

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-----Original Message-----
From: Nick Marentes <nickma2 at optusnet.com.au>
To: CoCoList <coco at maltedmedia.com>
Sent: Mon, Oct 20, 2014 5:15 am
Subject: Re: [Coco] Access to 225 lines in BASIC


On 20/10/2014 7:00 AM, Nick Marentes wrote:
> I am creating a program in BASIC but I require the use of more 
> vertical screen space than what BASIC allows.
>
> Basic restricts all graphics (HSCREEN2) to a maximum of 192 vertical 
> lines yet the display can be extended up to 255 (with a POKE).
>
> The BASIC drawing commands restrict their drawing to 192 although they 
> accept values up to 255 (I think) but truncate to 192.
>
> Are there any magical POKEs to BASIC that allow it to draw up to the 
> maximum?
>
> Nick
>


Call the search off. I found it. It was in the "CoCo III Secrets 
Revealed" book.

POKE&HE06C,&H35
POKE&HE06D,&H3E
POKE&HE06E,&H34
POKE&HE06F,&H3D
POKE&HEB75,199
POKE&HE7BA,200
POKE&HE7BE,199
POKE&HEF8F,18

This allows BASIC to draw down to 200 lines (Actually 201 lines).

I fiddled with the numbers and I actually got it down to 204 lines but I 
needed 208 as a minimum. This required setting the screenmode to 225 
scanlines but BASIC could only handle up to 204.

I wonder why the Super Extended Basic designers forced it to 192 when it 
could have easily done 200. Maybe to keep it consistant with the VDG 
modes max of 192?

Nick


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