Atari 800

PENH (Light Pen Horizontal Color Clock Position)(D40C): This address
reads the Horizontal Light Pen Register (based on the horizontal color clock
counter in hardware). The values range from 0 to decimal 227. Wraparound
occurs when the pen if near the right edge of a standard-width screen. PENH
and PENV are modified when any of the joystick trigger lines is pulled low.
D7 D6 D5 D4 D3 D2 D1 DO
H7 H6
H5
H4 H3 H2 H1 HO
OS SHADOW: LPENH (hex 234)
PENV (Light Pen Vertical TV Line Position)(D40D): This address reads
the Vertical Light Pen Register (8 most significant bits, same as VCOUNT).
D6
D5
D4
D3
LP8 7
6
5 4
D2
D1
3
2
DO
1 0 LPO not read. Two line
resolution supplied.
OS SHADOW: LPENV (hex 235)
Front Panel (Controller) Jacks as I/O Parts:
PIA (6520/6820)
Out: TTL levels, 1 load
In : TTL levels, 1 load
Port A Circuit (typical):
~-----f
- . ..:.L. • 001
6520
(A) I
Port
220
T
Port B Circuit
6520
.001
"Trigger" Port Circuit (typical):
CTIA Trig 220
1\/V\J.-~---1
l .001
T
III. 23
Jack
Jack
Jack