GENPAT command

Characters on a type 3 screen occupy 8 x 20 pixels, therefore it needs 20 bytes to define their shape. The GENPAT command only specifies 8 bytes, therefore three GENPAT commands are needed to completely redefine the shape of a character. The format of the command is:

GENPAT p,n,d1,d2,d3,d4,d5,d6,d7,d8

In this command p=0 to redefine rows 1 to 8 of a character, p=1 to redefine rows 9-16 of a character and p=2 to redefine rows 17-20 of the character.

n is the ASCII code of the character to redefine (0-255).

d1 to d8 are the bytes defining successive rows. For p=2, d5 to d8 are ignored, but must be present.

Type 2 screens use the same font as type 3, but only uses every other row to give an 8 x 10 character.

Redefining a character lasts for as long as a type 2 or type 3 screen is selected. Switching to a type 0 or 1 screen looses all the user definitions and characters will have their default shape when a type 2 or 3 screen is selected again.

GR$ function

The function GR$(x,y,n) returns a character whose ASCII value is made up of a column of n (1 to 8) plot-points, starting at the coordinate (x,y).

For type 2 screens, the plot-points may be the result of a character printed at that location, or of a point plotted there.

For type 3 screens, any location containing a printed character is regarded as having no plotted points.

SPK$ function

This function returns the character under the cursor, and advances the cursor.

For type 3 screens it returns the character at that location regardless of any attributes (such as inverse printing) that may have been applied. Any character location containing plotting will return an ASCII NULL (zero) character.

For type 2 screens it works by recognising the plot pattern at that location. It will therefore fail (and return ASCII NULL) if the character has been over-plotted, is inverse, or contains the underline cursor. It will however work for user-defined character shapes providing they are clear.

USER COLOUR command

Memotech Basic supports 16 colours, as generated by the VDP. However the Propeller VGA display is capable of generating 64 colours. By default 16 of these 64 colours which approximate to the VDP are used. However the USER COLOUR command provides the ability to change these. The format of this command is:

USER COLOUR c, r, g, b

Where:

c = Colour to redefine (0 to 15)

r = Red value for this colour (0 to 3)

g = Green value for this colour (0 to 3)

b = Blue value for this colour (0 to 3)

Note: This command will not change the colour of any text that is already displayed. The correct sequence is:

• Use the USER COLOUR command to to define the RGB values for a colour or colours.

• Use the INK and / or PAPER commands to select the newly defined colours.

• Print text.

By repeating this sequence all 64 colours may be displayed at the same time.

USER VGA command

This command enables you to use an 80 column screen for editing programs. The format of this command is:

USER VGA mode

where mode = 1 for 80 column editing, and mode = 0 to return to 40 column editing. The effect of selecting 80 column mode is to change the definitions of virtual screens 0, 1, 5 and 7 to be type 3 screens. As a result program listing and editing uses the 80 column screen type.

The default graphics virtual screen (VS 4) is changed to a type 2 screen. This does mean that sprites cannot be used without redefining the screen.

If 80 column mode is selected, it will also be used for PANEL, although that does not make any use of the extra screen space.

If you have two monitors attached to the Memotech, one on the original composite VDP output and a second on the CFX-II VGA output, then there are two further modes (mode =2 or mode = 3) that may be usefully selected. If these modes are selected, then the CFX-II display does not switch back to VDP echo mode when virtual screens of types 0 or 1 are selected. Instead it continues to display what was written to the type 2 or type 3 virtual screens. Thus it is possible to make use of both monitors by having some virtual screens of type 0 or type 1, which will be displayed on the composite video monitor, and other virtual screens of type 2 or 3 will be displayed on the VGA monitor.

The difference between VGA modes 2 and 3 is that in mode 2, virtual screens 0, 1, 5 and 7 default to type 0, so Basic editing and PANEL will be on the composite monitor, whereas in VGA mode 3 these virtual screens default to type 3, so that Basic editing and PANEL will be in 80 columns on the VGA monitor.

 

Summary of Control and Escape Codes

The following tables summarises the use of control and escape codes from within MTX Basic, the CP/M driver for the original Memotech 80 column card, and the CFX-II 80 column display. Note that when using the 80 column display from MTX Basic as described in the previous section the MTX ROM processes all the control and escape codes, so the first column of the tables is relevant. The third column is only applicable for CP/M, or bypassing the MTX ROM by writing to port 96 (60 hex).

Control Codes

Hex	Letter	MTX Basic	Memotech 80 Col	CFX-II VGA
0x01	A	Plots point	Plots point	Plots point
0x02	B	Plots line	Plots line	Plots line
0x03	C	Position cursor	Position cursor	Position cursor
0x04	D	Sets background colour	Sets background colour	Sets background colour
0x05	E	Erase to end of line	Erase to end of line	Erase to end of line
0x06	F	Sets foreground colour	Sets colours /attributes	Sets foreground colour
0x07	G	Sounds bell	Sounds bell
0x08	H	Backspace	Backspace	Backspace
0x09	I	Tab	Tab	Tab
0x0A	J	Line feed	Line feed	Line feed
0x0B	K	Cursor up	Cursor up	Cursor up
0x0C	L	Clear screen	Clear screen	Clear screen
0x0D	M	Carriage return	Carriage return	Carriage return
0x0E	N	CTLSPR	Blink on	Blink on
0x0F	O	GENPAT	Blink off	Blink off
0x10	P	COLOUR	Black foreground	Black foreground
0x11	Q	ADJSPR	Red foreground	Red foreground
0x12	R	SPRITE	Green foreground	Green foreground
0x13	S	MOVSPR	Yellow foreground	Yellow foreground
0x14	T	VIEW	Blue foreground	Blue foreground
0x15	U	Insert key	Magenta foreground	Magenta foreground
0x16	V	Delete key	Cyan foreground	Cyan foreground
0x17	W	Tab back	White foreground	White foreground
0x18	X	White text on black	Initialise configuration	Initialise configuration
0x19	Y	Cursor right	Cursor right	Cursor right
0x1A	Z	Home cursor	Home cursor	Home cursor
0x1B	[	Escape	Escape	Escape
0x1C	\	Scroll mode	Scroll mode	Scroll mode
0x1D	]	Page mode	Page mode	Page mode
0x1E	^	Show cursor	Show cursor	Show cursor
0x1F	_	Hide cursor	Hide cursor	Hide cursor

Escape Codes

Letter	MTX Basic	Memotech 80 Col	CFX-II VGA
A	ATTR	Select alternate font	Select alternate alpha font
B	Select language	Set bit of both attributes	Set bit of both attributes
C	GR$	Scroll mode	Scroll mode
D	Invalid	Page mode	Page mode
E	Invalid	Show cursor	Show cursor
F	Invalid	Hide cursor	Hide cursor
G	Invalid	Select graphics font	Select lower graphics font
H	Invalid		Delete character under cursor
I	Insert blank line	Insert blank line	Insert blank line
J	Delete the current line	Delete the current line	Delete the current line
K	Duplicates a line		Duplicates a line
L	Read character at cursor
M	Invalid		Redefine char.
N	Invalid	Set bit of non-printing attrib.	Set bit of non-printing attrib.
O	Invalid		Select virtual screen
P	Toggle Page / Scroll	Set bit of printing attributes	Set bit of printing attributes
Q	Invalid		Input 8-bit characters
R	Set print colour, clear attributes		Input raw buffer data
S	Invalid	Select standard font	Select standard alpha font
T	Invalid	Set printing attributes	Set printing attributes
U	Reset screen	Set non-printing attributes	Set non-printing attributes
V	BASIC setup	Set both attributes	Set both attributes
W	PANEL Setup	Set write mask	Set write mask
X	Simulate control code	Simulate control code	Simulate control code
Y	CRVS		Define virtual screen
Z	VS		Reboot
[
\
]
^			Copy characters
_			Space characters