Atari 800

ALLPOT (All Pot Lines Simultaneously)(D208): This address reads the
present state of the 8 line pot port.
pot
I D7
Pot
7
Capacitor dump tra n sitors
scan mode (bit 2 of SKCTL)
I
I
I
D6
I
DS D4 D3 D2
number:
6 5 4 3 2
8
Pot Line States
must be turned off by either going to fast
or starting pot scan (POTGO).
Dl
DO
1
0
0
1
Pot register value is valid.
Pot register value is not valid.
POTGO (Start Pot Scan)(D20B):
No
Data Bits Used
This write address starts the pot scan sequence. The pot values
(POTO - POT7) should be read first. This write strobe is then used causing
the following sequence.
1. Scan Counter cleared to zero.
2. Capacitor du~p transistors turned off.
3. Scan Counter begins counting.
4. Counter value captured in each of 8 registers (POTO -
POT7)
as each pot line crosses trigger voltage.
S. Counter reaches 228, capacitor dump transistors turned
on.
(Written to by OS vertical blank code)
TRIGO, TRIGl, TRIGZ, TRIG3 (Trigger Ports)(O DOlO, 1 DOll, 2 D012,
3
D013): These addresses read port pins normally connected to the joystick
controller trigger buttons.
Not Used
(Zero Forced) DO
0
1
button pressed
button not pressed
OS SHADOWS: STRIG0-3 (hex 284-287)
NOTE:
TRIGO thru TRIG3 are normally read directly by the microprocessor.
However, if bit 2 of GRACTL is 1, these inputs are latched whenever
they go to logic zero. These latches are reset (true) when bit 2
of GRACTL is set to 0.
III.22