Scrolling of screen

[Jamesapp]

Hello

 

i have a book on ti 99/4a graphics and sound. 
 

there is an advanced section that discusses screen scrolling. 
 

i just copied and ran a program that scrolls “this is a test of scrolling” on the screen 40 times without quotations

 

the program next asks if youd like to scroll the screen again

 

im interested in the way the ti scrolls text? And also the behavior of the cursor and input from keyboard etc. 
 

i have a nano peb and extended basic. I have no experience with assembly language. 
 

i just read online the input command has something to do with scrolling? 
 

there are a couple of more scrolling programs im gonna look at from the book

 

wondered if anyone can point me in a direction to learn the underpinnings of the cursor and scrolling behavior? 
 

it would also help me to try and understand ti basic in general. 
 

im not a great programmer. But im interested in how the os works. Are there levels to things like the interpreter or assembler? Is basic kind of on top of the os? 
 

anyway any info or thoughts would be great

[RXB]

Do you want the code for TI Basic or XB or for EA cartridge?

I have the source code for all of them and how they work.

[+videofx]

Hi RXB,

 

Thanks for your offer! I know I would be interested in the code for all the languages you mentioned. 

 

 

Thanks!

[Asmusr]

The screen is stored in 32x24=768 bytes of video (VDP) memory starting from address 0. Each byte represents one character. Scrolling the screen up is done by copying the 736 bytes from address 32 to address 0 and clearing the bottom line at address 736.

[+TheBF]

1 hour ago, Jamesapp said:

But im interested in how the os works. Are there levels to things like the interpreter or assembler? Is basic kind of on top of the os? 

Here is an overview of the TI-99 that might be of use.

https://www.unige.ch/medecine/nouspikel/ti99/architec.htm

 

Are there levels... ?   (Not an expert but here is how I understand the Software architecture)

 

The "O/S" is mostly the GPL (graphics programming language) as far as I know.  GPL is a virtual machine (VM) that has a claim to fame of running in a ridiculously small amount of RAM (<256 bytes) and using the Video processor RAM for everything else.  It uses byte codes for the VM instructions and so can squeeze a lot of program into a small space. 

On top of GPL, the "user interface" is TI-BASIC.  That's about it for "layers" I think.  Somebody else might have more insights.

Other cartridges may or may not use the GPL routines from the system. It's kind of up to the programmer.

 

The TI Assembler is a separate binary program. It converts Assembly language text to either a) tagged object code or b) a binary image

 

The loaders to get the object code or a binary program into RAM are in the "GROM" chip in the Editor Assembler Cartridge. (I believe)

 

Typically, when a binary program is loaded into memory it takes over the machine, so no O/S per se.

There are however routines in ROM that have some use for a binary program and there is also code in the disk controller card and other peripheral cards that are useable/callable by a program. 

 

That's a start.

[pixelpedant]

Most of this video is about scrolling techniques in XB and Compiled XB (via the XB Game Developer's Package). 

 

So this may be of interest:

 

 

 

[RXB]

4 hours ago, videofx said:

Hi RXB,

 

Thanks for your offer! I know I would be interested in the code for all the languages you mentioned. 

 

 

Thanks!

RXB has the XB GPL PRINT routine if you search the text files for PRINT in GROM 4 and Assembly version I created in ROM 3.

301101080_RXB2022E.zip