SCR0

SCR0 - Text Screen

[TOC]

Screen Buffer

This device is a text screen, with an horizontal resolution of 80 characters and vertical resolution of 25 characters. The screen buffer can be mapped to any address. At the moment, the code page used is Code Page 850, although that might change in the future.

One possibility might be allowing the programmer to overwrite the existing code page. At the moment, there is only one screen mode supported (80x25). But that might change in the future.

Each character takes 2 bytes:

:::text
7 6 5 4 3 2 1 0   7 6 5 4 3 2 1 0 
B [bkg] I [for]   [ code point  ]
|   |   |    |              !---- Character
|   |   |    !------------------- Foreground colour (Text colour)
|   |   !------------------------ Foreground Intensity (see below)
|   !---------------------------- Background colour
!-------------------------------- Blink (1-blink, 0-no blink)

Blinking is not yet supported in the Simulator. It will come in time.

The available colours are as follow:

Value	Colour
0x0	Black
0x1	Blue
0x2	Green
0x3	Cyan
0x4	Red
0x5	Magenta
0x6	Brown
0x7	White

For the foreground colour an extra bit (Foreground intensity) is available. It allows the foreground colour to be a brighter version of the colours in the above table.

Functions

Function 0 - Screen Information

Register	Meaning
Input
ip	Bus and function
Output
ip	Error code
r0	Address of the screen buffer
r1	Horizontal resolution (in characters)
r2	Vertical resolution (in characters)
r3	Bytes per character

Function 1 - Map screen buffer

This function allows mapping the screen buffer to a different address.

Register	Meaning
Input
ip	Bus and function
r0	Screen buffer address
Output
ip	Error code

Interrupts

This device doesn't generate any interrupts