Atari ST series Technical Reference Manual page 348

Header
IKBD status record
$F6
Absolute mouse position record
$F7
$F8-$FB Relative mouse position record (bits 0 and 1 indicate
button status)
$FC Time-of-day record
$FD Joystick report (both sticks)
$FE Joystick 0 event record
$FF Joystick 1 event record
Mouse Functions
The IKBD enables the ST mouse to operate in one of three
modes. In relative position mode (the default mode used by
TOS), the IKBD sends mouse position packets whenever a
mouse button is pressed or released, or moves more than a
prescribed threshold distance (which the user may set) in
any direction. The movement report is sent at full resolution,
not scaled to even multiples of the threshold distance. You
may designate whether you want to place the y origin at the
bottom (the ST default) or the top of the coordinate scheme.
If you place it at the top, downward motion is shown as pos­
itive, and upward motion as negative. If you place it at the
bottom, downward movement is negative, and upward
movement is positive.
The relative position may change by a value much
greater than the threshold distance if mouse reports have
been paused, or if the motion occurs while the IKBD is busy
reporting other events. If the accumulated motion exceeds
the +127 to -1 2 8 range of a single report, multiple reports
are sent.
The second mouse mode is absolute position mode. In
this mode, position reports are not sent until the user asks
for them, via an interrogate command. If the user so desig­
nates, position reports may also be sent when one of the
mouse buttons is pressed or released. The position reports
that are sent give the mouse position as absolute x,y coordi­
nates. These coordinates are tracked internally by the IKBD,
according to a user-designated scale factor which determines
how far the mouse has to move before an x or y value
changes. There is also a command for resetting the x,y posi­
tion.
The mode can also operate in keycode mode. In this
340
APPENDIX I
Information Packet Type