============================
QS Hi-Res Board for the ZX81
Quicksilva
============================

The QS Hi-Res Board ROM provides 14 commands that can be called from BASIC to
manipulate the hi-res display file. The command parser is invoked via a USR 10240
call and it will execute the hi-res commands specified in the REM statement that
follows in the next BASIC line.

A number of the commands require arguments to define the operation that they must
perform. These arguments must be set up within BASIC variables and then it is the
name of the variables that are specified as the command arguments.

Any number of commands may be included within a REM statement, each separated by
one or more spaces.

The available commands are:

BLACK      Selects the colour of the foreground pixels to black and hence the
           background colour to white, i.e. black-on-white.
WHITE      Selects the colour of the foreground pixels to white and hence the
           background colour to black, i.e. white-on-black.
CLEAR      Clears the hi-res display file to the active background colour.
MOVE x y   Move the current screen coordinates to the values held in the specified
           numeric variables.
PLOT x y   Plots the pixel at the coordinates held in the specified numeric
           variables.
DRAW x y   Draws a line from the current screen coordinates to the coordinates
           held in the specified variables
PRINT n$   Prints a message held in the specified string variable to the hi-res
           display at the row and column corresponding to the current screen
           coordinates.
SCROLL     Scrolls the bottom 24 lines (3 rows) of the hi-res display file up. The
           new screen coordinates are set to start of the last row of the display,
           i.e. the start of line 184.
UP         Scrolls the hi-res display file up. The top line of pixels are lost, and
           the bottom line of pixels are set to the background colour.
DOWN       Scrolls the hi-res display file down. The bottom line of pixels are lost,
           and the bottom line of pixels are set to the background colour.
LEFT       Scrolls the hi-res display file to the left. The leftmost column of
           pixels are lost, and the rightmost column line of pixels are set to the
           background colour.
RIGHT      Scrolls the hi-res display file to the right. The right most column of
           pixels are lost, and the leftmost column line of pixels are set to the
           background colour.
COPY       Copies all 192 lines of the hi-res display file to the ZX printer.
BOX x y    Draws a box spanning the current coordinates to the destination
           coordinates held in the specified numeric variables.

Only the first two letters of the name of a command are checked by the ROM and so
the names can be truncated to save memory.

The hi-res display file will be shown as soon as any of the hi-res commands are
executed.

After a program stops (due to ending, BREAK being pressed or an error occurring),
the hi-res display file will remain on screen. All BASIC error codes will appear on
the lo-res display and therefore will not be visible while the hi-res display is
being shown. Likewise, new commands typed in will not be visible while the hi-res
display is being shown.

Return to the normal lo-res display file is by pressing the Reset push button or by
typing: POKE 10240,0


ERROR CODES

G - Invalid command.
H - Invalid parameter.
I - Variable not found.


EXAMPLE

  10 LET H=10240
  20 LET A=0
  30 LET B=0
  40 LET X=255
  50 LET Y=191
  60 RAND USR H
  70 REM WHITE  CLEAR  MOVE A B  DRAW X Y
  80 RAND USR H
  90 REM MO A Y DR X B


SELF-TEST ROUTINE

The ROM for the QS Hi-Res board contains a self-test routine, which can be invoked
via RAND USR 10243. It will verify the on board 6K RAM is operational and will then
draw a test screen.


===============================================================================


TECHNICAL NOTES

Display file resolution: 256 x 192
Display file structure : 32 bytes x 192
Display file size      : 6144 bytes
Display file location  : $A000-$B7FF held in on board 6K RAM

Read from $2000-$2FFF (A13 = 1) selects the hi-res display mode.
Write to $2000-$2FFF (A13 = 1) selects the normal display mode.

Push button forces a return back to normal display mode.

The 2K ROM appears at $2800-$2FFF.


COMMERCIAL PROGRAMS RELEASED FOR THE QS HI-RES BOARD

- ZX Chess II (Artic Computing Ltd)