012- How do I write programs which use the mouse?
Description
This article is from the Apple II Programming FAQ, by Jeff Hurlburt with numerous contributions by others.
012- How do I write programs which use the mouse?
The assembly language interface to the mouse firmware is documented in
three places:
- the reference material that was supplied with the AppleMouse card
for the IIe.
- the IIc Technical Reference Manual.
- the IIgs Firmware Reference Manual.
Interfacing to the mouse is somewhat complicated, especially if you
want to implement some kind of mouse cursor (usually requires writing
an interrupt handler).
The first problem is locating the mouse firmware. It could be in any
slot for a IIe or IIgs, or either of two slots for the IIc. The safest
method is just to do a slot search, looking for the mouse ID bytes:
$Cn05 = $38
$Cn07 = $18
$Cn0B = $01
$Cn0C = $20
$CnFB = $D6
On a ROM 3 IIgs, it is possible that the mouse firmware will not be
available, because this doesn't prevent the use of the mouse from
GS/OS (the Miscellaneous Toolset or Event Manager can still be
used). An AppleMouse card, if installed, is not used by the toolbox.
On a ROM 1 IIgs, the slot mouse firmware is used by the toolbox, so
slot 4 must be set to "Mouse Port", or an AppleMouse card may be
installed in any slot.
Using the mouse firmware consists of calling the various parameters
provided by the firmware. An entry point table is provided in the
mouse slot. The routines common to all implementations are:
$Cn12 SETMOUSE Sets mouse mode
$Cn13 SERVEMOUSE Services mouse interrupt
$Cn14 READMOUSE Reads mouse position
$Cn15 CLEARMOUSE Clears mouse position to 0 (for delta mode)
$Cn16 POSMOUSE Sets mouse position to a user-defined pos
$Cn17 CLAMPMOUSE Sets mouse bounds in a window
$Cn18 HOMEMOUSE Sets mouse to upper-left corner of clamp win
$Cn19 INITMOUSE Resets mouse clamps to default values;
sets mouse position to 0,0
Each of the above locations contains the low byte of the entry point
for the routine. The high byte is $Cn. The usual method for calling
these routines is to set up a single subroutine which is patched with
the location of the appropriate routine as required. You could also
set up a series of subroutines for calling each routine.
The general logic would be as follows:
Locate the mouse slot by searching for the ID bytes described
earlier. Patch the slot into the following routine:
TOMOUSE LDX #$C1 ; Patch operand byte with slot in $Cn form
LDY #$10 ; Patch operand byte with slot in $n0 form
JMP $C100 ; Patch high byte of operand with slot in
; $Cn form. Low byte of operand must be
; patched with entry point from table above
You should also set up a pair of locations on zero page containing
$Cn00, which will be used to look up the table. You can then have code
as follows to call each of the routines:
MOUSEPTR EQU $00 ; (or some other pair of zero page locations)
SETMOUSE
LDY #$12 ; Offset to entry point
BNE GOMOUSE ; Go to the mouse routine - always taken
SERVEMOUSE
LDY #$13 ; Offset to entry point
BNE GOMOUSE ; Go to the mouse routine - always taken
[etc. - one routine for each mouse call you will be using]
GOMOUSE TAX ; Preserve the value in A
LDA (MOUSEPTR),Y ; Get the routine entry point
STA TOMOUSE+5 ; Patch the JMP instruction
TXA ; Restore the value in A
; The following operand bytes must be patched by the
; initialization code which detects the mouse.
TOMOUSE LDX #$C1 ; Set up slot in $Cn form in X
LDY #$10 ; Set up slot in $n0 form in Y
JMP $C100 ; Go to the mouse routine
With code like the above, your program can just use JSR INITMOUSE,
etc. to call the appropriate routine.
The mouse routines make use of screen holes for the slot containing
the mouse interface firmware/card. The screen holes are as follows:
$0478 + slot Low byte of absolute X position
$04F8 + slot Low byte of absolute Y position
$0578 + slot High byte of absolute X position
$05F8 + slot High byte of absolute Y position
$0678 + slot Reserved and used by the firmware
$06F8 + slot Reserved and used by the firmware
$0778 + slot Button 0/1 interrupt status byte
$07F8 + slot Mode byte
You can access the screen holes by getting the mouse slot number in
the $Cn form (LDX TOMOUSE+1), then indexing off the above locations
minus $C0 with X (or just AND the value with $0F and use the base
addresses directly).
The screen holes should be used only as specified by the mouse
routines below. You should never write to them, except as specified by
POSMOUSE.
The interrupt status byte is defined as follows:
Bit 7 6 5 4 3 2 1 0
| | | | | | | |
| | | | | | | \--- Previously, button 1 was up (0) or down (1)
| | | | | | \----- Movement interrupt
| | | | | \------- Button 0/1 interrupt
| | | | \--------- VBL interrupt
| | | \----------- Currently, button 1 is up (0) or down (1)
| | \------------- X/Y moved since last READMOUSE
| \--------------- Previously, button 0 was up (0) or down (1)
\----------------- Currently, button 0 is up (0) or down (1)
(Button 1 is not physically present on the mouse, and is probably
only supported for an ADB mouse on the IIgs.)
The mode byte is defined as follows.
Bit 7 6 5 4 3 2 1 0
| | | | | | | |
| | | | | | | \--- Mouse off (0) or on (1)
| | | | | | \----- Interrupt if mouse is moved
| | | | | \------- Interrupt if button is pressed
| | | | \--------- Interrupt on VBL
| | | \----------- Reserved
| | \------------- Reserved
| \--------------- Reserved
\----------------- Reserved
The button and movement status are only valid after calling
READMOUSE. Interrupt status bits are only valid after SERVEMOUSE and
are cleared by READMOUSE. The appropriate screen hole information must
be copied elsewhere before enabling interrupts with CLI or PLP.
The routines are used as follows. X and Y must be set up with $Cn and
$n0 in all cases. Interrupts must be disabled before calling any of
these routines. Assume all registers are scrambled on exit unless
otherwise noted.
SETMOUSE
Sets mouse operation mode.
Entry: A = mouse operation mode ($00 to $0F) - see mode byte.
Exit: C = 1 if illegal mode entered.
Screen hole mode byte is updated.
SERVEMOUSE
Tests for interrupt from mouse and resets mouse's
interrupt line.
Exit: C = 0 if mouse interrupt occurred.
Screen hole interrupt status bits are updated to show
current status.
READMOUSE
Reads delta (X/Y) positions, updates absolute X/Y pos,
and reads button statuses from the mouse.
Exit: C = 0 (always).
Screen hole positions and button/movement status bits are
updated, interrupt status bits are cleared.
CLEARMOUSE
Resets buttons, movement and interrupt status 0.
(This routine is intended to be used for delta mouse
positioning instead of absolute positioning.)
Exit: C = 0 (always).
Screen hole positions and button/movement status bits are
updated, interrupt status bits are cleared.
POSMOUSE
Allows caller to change current mouse position.
Entry: Caller places new absolute X/Y positions directly in
appropriate screen holes.
Exit: C = 0 (always).
Screen hole positions may be updated if necessary (e.g.
clamping).
CLAMPMOUSE
Sets up clamping window for mouse user. Power up default
values are 0 to 1023 ($0000 to $03FF).
Entry: A = 0 if entering X clamps, 1 if entering Y clamps.
Clamps are entered in slot 0 screen holes as follows.
NOTE: these are NOT indexed by the mouse slot number.
$0478 = low byte of low clamp.
$04F8 = low byte of high clamp.
$0578 = high byte of low clamp.
$05F8 = high byte of high clamp.
Exit: C = 0 (always).
Screen hole position is set to top left corner of clamping
window for the IIgs.
Note: The IIgs automatically homes the mouse when this call is
made, but this doesn't happen for the IIc and AppleMouse
card.
HOMEMOUSE
Sets the absolute position to upper-left corner of
clamping window.
Exit: C = 0 (always).
Screen hole positions are updated.
INITMOUSE
Sets screen holes to default values and sets clamping win
to default value of 0 to 1023 in both X and Y directions,
resets hardware.
Exit: C = 0 (always).
Screen holes are updated.
The general method of using the mouse firmware is as follows:
- Call SETMOUSE specifying a mode of 1 (enabled, no interrupts).
- Call INITMOUSE.
- Call CLAMPMOUSE to set up the required clamps (once per ea axis).
- If necessary, call SETMOUSE again with the actual mode you want.
You must set up a ProDOS interrupt handler if you want to use the
interrupt modes.
If you are using polled mode, call READMOUSE as required to update the
mouse position and button status information.
If you are using interrupt mode, your interrupt handler should call
SERVEMOUSE to check for a mouse interrupt. If none occurred, return to
ProDOS with C=1. If one did occur, note the type of interrupt (if
necessary), then call READMOUSE to the new position information, and
copy the data elsewhere. Finally, return to ProDOS with C=0.
When your program is finished, it should disable the mouse by using
SETMOUSE with A=0, and remove the interrupt handler (if
necessary). --David Empson
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