Digital Video
LIGHT PEN
(JLPEN)
The remaining
8
bits of digital video are available on this connector.
The signals are Red 0-2 (pins
2,
3,4),
Green 0-2 (pins
6,
7,
8).
and
Blue 1-2 (pins 10 and 1 1). The timing of the digital video
is
not
tightly specified. Developers wishing to use this should contact Com-
modore for further details.
This
is
an input to the Agnus light pen input. This signal should go
low in response to the lighting of a pixel on a video display monitor.
The Agnus chip latches the raster position that was in effect when
the ILPEN signal goes low, so an application can follow the position
of a light pen on the screen. Pin
19.
PORT CONNECTIONS
Most of the signals from the bidirectional parallel port (printer port)
are available on this connector as well, along with a few others.
8
Bit Parallel Port
(PDO-PD7)
The
8
bit bidirectional parallel port most commonly used to drive a
Centronics interface printer externally is accessable here.
It
can be
used to control various aspects of a complex video interface device.
The port lines PDO-PD7 are on pins 23 to
30
of this connector.
Parallel Port Handshake
This
is
the acknowledge (IACK) input, the same as the acknowledge
(JACK)
input to the parallel port. Driving this with an output from a Video
Card can cause
a
level 2 interrupt to occur through the 8520 CIA de-
vice this is connected to, based on the programming of an
8520
reg-
ister. On pin 20.
Other Port Lines (BUSY,
Connector pins 18 (BUSY) and 16 (POUT) are general purpose 110
POUT, SEL)
signals that together can also function as a synchronous serial data
port driven by an 8520 CIA device. In normal printer use, the BUSY
signal is used to indicate printer buffer full to the Amiga, while POUT
is used to indicate the printer paper
is
out. For serial port usage,
BUSY
is
the serial clock, POUT
is
the serial data line. These should be
driven with open collector devices if the Video Card uses them as in-
puts to the 8520. The
SEL
signal, on pin 21, is a general purpose I10
port, usually used as a device select signal on the parallel port.
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