Memotech Compact Flash System - Version 2

CFX - II Video Modes

MTX CFX Boot Screen

CF Card Directory

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Video Modes and their usage

Bill has documented the video modes available in CFX-II in an Open Office document and a PDF - I have transcribed the content on this page.

CFX-II Video Modes

Bill Brendling 15 April 2020

Introduction

The VGA output from the CFX-II board is produced by a Parallax Propeller microcontroller chip. This supports a number of different operating modes:

• 80 x 24 text modes with 160 x 96 graphics, largely similar to the Memotech 80 column card:
  • 16 colour mode compatible with the Memotech card using colour output.
  • Monochrome (green) mode compatible with the Memotech card using monochrome output.
  • Enhanced 64 colour mode.
• 320 x 240 graphics mode with 40 x 24 text:
• 2 out of 64 colours per character cell.
• MTX VDP emulation mode:
  • Text mode: 40 x 24 characters.
  • Graphics mode I: 256 x 192 graphics, 2 out of 16 colours per 16 character cells.
  • Graphics mode II: 256 x 192 graphics, 2 out of 16 colours per character cell.
  • Multi-colour mode: 80 x 48 independent colour tiles.

CP/M Display

In CP/M mode character sequences for display are sent to the Propeller video generator. Processing of control and escape sequences is performed by the Propeller firmware on the CFX-II card rather than by a CP/M driver such as that for the original Memotech 80 column card.

Mode Selection

The CFX-II starts in 80 column, 16 colour mode compatible with the original Memotech 80 column driver. The following character sequences (escape codes) are used to switch between modes:  

Character Sequence	Mode Selected
0x1B, 0x9B	VDP emulation
0x1B, 0x9C	Compatible: 24 row x 80 column text, 16 colours, 160 x 96 graphics
0x1B, 0x9D	Monochrome: 24 row x 80 column text, monochrome green, 160 x 96 graphics
0x1B, 0x9E	Enhanced: 24 row x 80 column text, 64 colours, 160 x 96 graphics
0x1B, 0x9F	Graphics: 24 row x 40 column text, 64 colours, 320 x 240 graphics

These escape sequences do nothing on the original MTX, and have been chosen as unlikely to be generated accidentally. Note that the second character has to be exactly as given, none of the other characters with the same 5 lsb work (unlike most escape codes on the MTX).

Entering VDP emulation mode takes a few seconds and video generation is interrupted during the transition. Once the emulation has started the emulated VDP is still not configured with the MTX font, and shows a blank (red) screen. It then needs to be configured by writes to ports 0x01 and 0x02, as per the VDP. Once in VDP mode, this mode can only be exited by resetting the Propeller by a command to port 0x61 (see later), again causing an interruption to video generation.

Printable Characters (0x20 – 0xFF)

Typically a printable character will be displayed upon the screen, using the current printing attributes, and the cursor advanced one space. This may be affected by the write mask (Esc “W”). If this is set, the character may be updated, without changing the existing on-screen attributes, or the attributes may be updated without changing the displayed character.

If the cursor goes beyond the bottom of the screen, either the display will scroll (scroll mode) or the cursor will return to the top of the screen (page mode). There is nothing in the driver to pause and wait for a key press at the end of a page. This functionality must be at a higher level.

The CFX-II video has 256 character glyphs, illustrated in the figure below and an additional 256 plotting glyphs (the same as the Memotech 80 column card). Assuming that a character is output, the glyph displayed depends upon the font selected, and whether or not the graphics mode bit is set in the attribute byte.

If the graphics mode bit is clear, then the following table gives the glyph displayed:

Character Code	Standard Font	Alternate Font	Special Graphics Font
0x20 - 0x3F	Standard numerals (glyphs 0x20-0x3F)	Alternate numerals (glyphs 0xA0-0xBF)	Standard numerals (glyphs 0x20-0x3F)
0x40 - 0x5F	Standard upper case (glyphs 0x40-0x5F)	Alternate upper case (glyphs 0xC0-0xDF)	Special graphics (lower) (glyphs (0x00-0x1F)
0x60 - 0x7F	Standard lower case (glyphs 0x60-0x7F)	Alternate lower case (glyphs 0xE0-0xFF)	Special graphics (upper) (glyphs 0x80-0x9F)
0x80 - 0x9F	Special graphics (upper) (glyphs 0x80-0x9F)	Special graphics (upper) (glyphs 0x80-0x9F)	Special graphics (lower) (glyphs 0x00-0x1F)
0xA0 - 0xBF	Alternate numerals (glyphs 0xA0-0xBF)	Alternate numerals (glyphs 0xA0-0xBF)	Standard numerals (glyphs 0x20-0x3F)
0xC0 - 0xDF	Alternate upper case (glyphs 0xC0-0xDF)	Alternate upper case (glyphs 0xC0-0xDF)	Special graphics (lower) (glyphs 0x00-0x1F)
0xE0 - 0xFF	Alternate lower case (glyphs 0xE0-0xFF)	Alternate lower case (glyphs 0xE0-0xFF)	Special graphics (upper) (glyphs 0x80-0x9F)

It should be noted that character code 0x7F is printable.

It does not delete the character under the cursor. If the graphics mode attribute is set, then the corresponding plotting glyph is displayed. Each of the plotting glyphs consists of a 4x2 array of plot points as below, with the point filled if the corresponding bit is set, or clear if the bit is not set.  

Control Codes (0x00 – 0x1F)

Control codes may be followed by one or more data bytes update the display in various ways, as detailed in the following table. Any screen updates are affected by the settings of the write mask, as for the printable characters. Some of the details depend upon the currently selected mode (C=Compatible, M=Monochrome, E=Enhanced, G=Graphics).

Mode	Control Code	Data Bytes	Action
CMEG	^@ (0x00)		Does nothing
CME	^A (0x01)	m, n	Plot a point at x = m – 32, y = n – 32 If x < 0, x > 159, y < 0 or y > 95 do nothing.
G	^A (0x01)	xl, xh, y	Plots a point at x = 256 * xh + xl, y If x < 0, x > 319, y < 0 or y > 239 do nothing.
CME	^B (0x02)	m1, n1,  m2, n2	Draws a line from x1 = m1 -32, y1 = n1 – 32 to x2 = m2 – 32, y2 = n2 - 32
G	^B (0x02)	x1l, x1h, y1, x2l, x2h, y2	Draws a line from x1 = 256 * x1h + x1l, y1 to x2 = 256 * x2h + x2l, y2
CMEG	^C (0x03)	m, n	Sets cursor position: row = m – 32, column = n - 32
C	^D (0x04)	m	Set background colour (printing and non-printing): Bit 0 = Red, Bit 1 = Green, Bit 2 = Blue
M	^D (0x04)	m	Set the following attributes (printing and non-printing): Bit 1 = Inverse video Bit 2 = Shaded background
EG	^D (0x04)	m	Set background colour (printing and non-printing): Bits 0 & 1 = Red, Bits 2 & 3 = Green, Bits 4 & 5 = Blue
CMEG	^E (0x05)		Erase to end of line. Fill from cursor position to end of line with space character and non-printing attribute.
C	^F (0x06)	m	Set colours and attributes (printing and non-printing): Foreground: Bit 0 = Red, Bit 1 = Green, Bit 2 = Blue Background: Bit 3 = Red, Bit 4 = Green, Bit 5 = Blue Attributes: Bit 6 = Blink, Bit 7 = Plotting
M	^F (0x06)	m	Set attributes (printing and non-printing): Bit 0 = Underline, Bit 2 = Bright, Bit 4 = Inverse video, Bit 5 = Shaded background, Bit 6 = Blink, Bit 7 = Plotting
EG	^F (0x06)	m	Set foreground colour (printing and non-printing): Bits 0 & 1 = Red, Bits 2 & 3 = Green, Bits 4 & 5 = Blue
CMEG	^G (0x07)		Does nothing
CMEG	^H (0x08)		Moves the cursor back one space. If at the beginning of a line, moves back to the end of the previous line. If at top of screen, does nothing. Does not erase the character.
CMEG	^I (0x09)		Tab. Moves the cursor forward to the next multiple of 8 columns. If in the last 7 columns of a line moves to the start of the next line.  If in last 7 characters of screen, either scrolls a line, or moves to top of screen, depending upon scroll / page mode.
CMEG	^J (0x0A)		Cursor down. Moves the cursor down one line. If on last line of screen, either scrolls a line, or moves to top of screen, depending upon scroll / page mode.
CMEG	^K (0x0B)		Move cursor up one line. If already at top of screen, do nothing.
CMEG	^L (0x0C)		Clear screen. Fill entire video RAM with space character and non-printing attribute (depending upon write mask). Sets top of screen to top of video RAM.
CMEG	^M (0x0D)		Carriage return. Sets cursor position to beginning of line.
CMEG	^N (0x0E)		Blink on. Sets the blink bit (bit 6) in the printing attributes byte only.
CMEG	^O (0x0F)		Blink off.  Clears the blink bit (bit 6) in the printing attributes byte only.
CEG	^P (0x10)		Set print foreground colour to black.
M	^P (0x10)		Print attributes: Underline and bright off.
CEG	^Q (0x11)		Set print foreground colour to red.
M	^Q (0x11)		Print attributes: Underline on, bright off.
CEG	^R (0x12)		Set print foreground colour to green.
M	^R (0x12)		Print attributes: Underline and bright off
CEG	^S (0x13)		Set print foreground colour to yellow.
M	^S (0x13)		Print attributes: Underline on, bright off.
CEG	^T (0x14)		Set print foreground colour to blue.
M	^T (0x14)		Print attributes: Bright on, underline off.
CEG	^U (0x15)		Set print foreground colour to magenta.
M	^U (0x15)		Print attributes: Bright and underline on.
CEG	^V (0x16)		Set print foreground colour to cyan.
M	^V (0x16)		Print attributes: Bright on, underline off.
CEG	^W (0x17)		Set print foreground colour to white.
M	^W (0x17)		Print attributes: Bright and underline on.
CMEG	^X (0x18)		Initialise display: Turns on scroll mode. Sets both printing and non-printing colours to green foreground on black background. Turns on the cursor. Enables both character and attribute writes. Performs a carriage return and line feed. Selects the standard font.
CMEG	^Y (0x19)		Cursor forward. If in the last column of a line moves to the start of the next line.  If in last character of screen, either scrolls a line, or moves to top of screen, depending upon scroll / page mode.
CMEG	^Z (0x1A)		Home cursor. Moves cursor position to first character of top row.
CMEG	^[ (0x1B)		Start of an escape sequence. See next section.
CMEG	^\ (0x1C)		Sets scroll mode. If cursor flows off the bottom of the screen, then all text is moved up one line, bottom line is cleared (using space character and non-printing attribute, depending upon write mask), and cursor is positioned on the new bottom line.
CMEG	^] (0x1D)		Sets page mode. If cursor flows off bottom of screen it re-appears at the top of the screen. None of the screen is cleared. There is no code in the driver to wait for a key press.
CMEG	^^ (0x1E)		Turn on display of the cursor position.
CMEG	^_ (0x1F)		Turn off display of the cursor position.

Escape Sequences

Escape sequences are similar to control codes. They consist of the ESC character (0x1B), followed by the command character and then possibly one or more data bytes.

In the Memotech implementation, if the character following the ESC is in the range 0x00 – 0x1F then the sequence is terminated and does nothing. Otherwise the 5 lsb of the command character are used to select the command to be executed. Therefore the sequence (ESC, 0x01) does nothing while each of the sequences (ESC, “!”), (ESC, “a”), (ESC, 0x81), (ESC, 0xA1), (ESC, 0xC1) and (ESC, 0xE1) all do the same as (ESC, “A”). In the table below, the standard upper case command character is listed, but the descriptions are applicable to all the other equivalents.  

Mode	Command Character	Data Bytes	Action
CMEG	@ (0x40)		Does nothing.
CMEG	A (0x41)		Selects alternate font (see section on printable characters)
C	B (0x42)	m	Clears or sets print and non-print colour and attribute bits according to m = “0” (0x30) to m = “8” (0x38): “0”: Clear. Black foreground and background. “1”: Set red foreground bit. “2”: Set green foreground bit. “3”: Set blue foreground bit. “4”: Set red background bit. “5”: Set green background bit. “6”: Set blue background bit. “7”: Set blink bit. “8”: Set plot glyphs bit.
M	B (0x42)	m	Clears or sets print and non-print attribute bits according to m = “0” (0x30) to m = “8” (0x38): “0”: Clear. Green on black text. “1”: Set underline bit. “2”: No effect. “3”: Set bright bit. “4”: No effect. “5”: Set inverse video bit. “6”: Set shaded background bit. “7”: Set blink bit. “8”: Set plot glyphs bit.
EG	B (0x42)	m	Clears or sets print and non-print attribute bits according to m = “0” (0x30) to m = “8” (0x38): “0”: Clear. All attributes off. “1”: Set underline bit. “2”: No effect. “3”: No effect. “4”: No effect. “5”: Set inverse video bit. “6”: Set XOR drawing bit. “7”: Set blink bit. “8”: Set plot glyphs bit.
CMEG	C (0x43)		Sets scroll mode.
CMEG	D (0x44)		Sets page mode.
CMEG	E (0x45)		Turn on display of the cursor position.
CMEG	F (0x46)		Turn off display of the cursor position.
CMEG	G (0x47)		Selects special graphics font (see section on printable characters).
CMEG	H (0x48)		Deletes character under cursor.
CMEG	I (0x49)		Moves all the text on the line containing the cursor and below down one line. The bottom line is lost. The line containing the cursor is cleared (using space character and non-printing attribute). The cursor retains its previous position (on the now blank line).
CMEG	J (0x4A)		Moves all text in lines below the cursor up one line. The new bottom line is cleared (using space character and non-printing attribute). The cursor retains its previous position.
CMEG	K (0x4B)		Duplicate the line containing the cursor on the next line down, pushing all lines below it down one line. The bottom line is lost. The cursor retains its previous position.
CMEG	L (0x4C)		Does nothing.
CMEG	M (0x4D)	n, m, p0, p1, p2, p3...	Redefine a character glyph. Each glyph is defined by five blocks of four rows of eight pixels. Therefore each block requires four bytes to redefine. n = Character glyph to redefine. m = Contains three bit fields: Bit 0: 0 = Text glyph, 1 = Graphics glyph. Bits 1-3: First block to redefine (0-4). Bits 4-6: Number of consecutive blocks to redefine. Bit 7: Unused. p1… = Bytes defining the pixels to set in successive rows of the glyph.
CMEG	N (0x4E)	m	Sets colour and attributes as per “<Esc>B” except only affects non-print output.
CMEG	O (0x4F)	m	Selects virtual screen 0 – 7 given by bottom 3 bits of m. Note: These virtual screens are not the same as those from Basic.
CMEG	P (0x50)	m	Sets colour and attributes as per “<Esc>B” except only affects print output.
CMEG	Q (0x51)	n, d1...	Input a number of 8-bit glyph codes without them being interpreted as control and escape sequences. n = Number of following byte glyph codes. d1 … = Bytes to display.
CMEG	R (0x52)	n, d1...	Input a number of characters in the video generator internal format (documented in the following section). n = Number of characters to input in raw internal format. d1… - Bytes forming each character. Four bytes per character for CME modes, ten bytes per character for G mode.
CMEG	S (0x53)		Selects standard font (see section on printable characters)
C	T (0x54)	m	Sets the printing colour and attributes according to the bits of m: Bit 0: Red foreground. Bit 1: Green foreground. Bit 2: Blue foreground. Bit 3: Red background. Bit 4: Green background. Bit 5: Blue background. Bit 6: Blink. Bit 7: Plotting glyphs.
M	T (0x54)	m	Sets the printing attributes according to the bits of m: Bit 0: Underline. Bit 1: No effect. Bit 2: Bright text. Bit 3: No effect. Bit 4: Inverse video. Bit 5: Shaded background. Bit 6: Blink. Bit 7: Plotting glyphs.
EG	T (0x54)	m	Sets the printing attributes according to the bits of m: Bit 0: Underline. Bit 1: No effect. Bit 2: No effect. Bit 3: No effect. Bit 4: Inverse video. Bit 5: XOR printing. Bit 6: Blink (Enhanced mode only). Bit 7: Plotting glyphs.
CMEG	U (0x55)	m	As per “<Esc>T” but sets the non-print colours and attributes.
CMEG	V (0x56)	m	As per “<Esc>T” but sets both the print and non-print colours and attributes.
CMEG	W (0x57)	m	Sets the write mask: If m = “0” (0x30) enable both character and attribute writes. If m = “1” (0x31) disable attribute writes. If m = “2” (0x32) disable character writes. Any other value of m has no effect.
CMEG	X (0x58)	m	Simulate the effect of the control code given by m & 0x1F.
CMEG	Y (0x59)	n, x, y, w, h	Define a virtual screen: n = Virtual screen number (0 to 7). x = Leftmost column position (0 to 79). y = Top row position (0 to 23). w = Width (0 to 80 – x). h = Height (0 to 24 – y). Note this is not the same as the Basic CRVS.
CMEG	Z (0x5A)		Restarts the CFX-II video generator.
CMEG	[ (0x5B)		Does nothing.
CMEG	\ (0x5C)		Does nothing.
CMEG	] (0x5D)		Does nothing.
CMEG	^ (0x5E)	n, x1, y1,  x2, y2	Copies n characters from position x1, y1 to position x2,y2 without moving the cursor.
CMEG	_ (0x5F)	n, x, y	Blanks n characters at position x, y without moving the cursor.