Atari 800

INTERRUPT
SUMMARY
I
I I
STATUS
I
I
NAME
FUNCTIONS
I
ENABLE
I
STATUS
RESET
I
I I I
I
I
Display
I
NMIEN
I
NMIST Address
I
I
NMI
Instruction I (Bits 6 thru 7) I (Bits 5 thru
7)
NMIRES
I
I
INTERRUPTS
Vert.
Blank
I
Normally Zero Nol.:'mally Zero (R ~ sets all NMI
I
I
Reset Button
I
~Disabled)
~no interruEt)
status
together) I
I I
I
I
KEYS
I
IRQ EN
IRQST
Reset
(to true) I
I
Serial I (Bits 0 thru
7)
(Bits 0 thru
7)
By Zero in
I
I
Eorts
I
zero is
Normally True Corresponding
I
I
Timers
I
(Disabled)*
(no interrupt)
Bit of IRQEN
I
I
I
~exceEt Bit 3)*1
I
IRQ
I
I
INTERRUPTS
Peripheral
I
DO of PACTL D7 of PACTL Reset by .
I
A
!Normally Zero !Normally Zero
Reading PORT
I
I
~Disabled)
l{no interruEt)
Register
I
I I
I
Peripheral I DO of PBCTL I D7 of PBCTL
Reset by
I
B !Normally Zero
!Normally Zero
Reading PORT
I
I
{Disabled)
I {no interruEt)
Register
E. CONTROLLERS
A variety of controllers can be plugged into the four jacks on the
front of the console. This includes joysticks, paddle (pot), twelve-key
keyboard, and light pen (when available).
A
B
The
controller ports are read through the PORTA and PORTB regisers
and the POT and TRIG registers. The OS reads these registers during
vertical blank and stores into its own RAM locations. These are STICK,
PADDLO through PADDL7, PTRIG'S and STRIG'S. The OS sets up PORTA AND
PORTB for input. This is done by setting PACTL or PORTB (Port Control)
bit 2 to a 0 (to select the dire~tion control register), then writing all
O's to the desired port. PACTL (PBCTL) bit 2 is then changed back to
a 1, allowing the program to read from the port. The ports can also be
I
I
I
I
I
I
I
I
set up for output by writing 1's instead of O's while the direction control
mode is selected.
Joysticks: The joysticks have four switches, one each for right (R),
left (L), back (B) and forward (F).
These switches are read through PORTA and PORTB. A fifth switch is
activated by pressing the red trigger button. The trigger buttons are
read from TRIGO through TRIG3. A value of 0 indicates that a button has
been pressed and a 1 indicates that it has not been pressed.
II. 30