Digital Output Ports:
P0~P5 may be used as general-purpose logic outputs to control circuitry external to the BOB-3 module. These are
unbuffered 200uA CMOS outputs; don’t attempt to drive heavy loads such as LEDs without buffering. See
{O
commands for application programming details.
Alternate port output signals, selected by software, may be used in external video processing circuitry as shown in
the drawing below. CSYNC (composite sync) may be used independently, to develop clamp pulses for DC
restoration, etc. Note that CSYNC is reserved for use with external circuitry that must be installed to use the text
crawl feature of BOB-3 modules with firmware version 2.00 or higher.
Variable Transparency:
BOB-3 supports manually variable video overlay transparency, but this feature requires a bit of external application
circuitry. The circuit below is an example of what’s necessary:
+5V
J1
BNC/RCA
1
2
Q1
2N3904
BOB-3 pin 3
R1
75
R2
100
EN
+
-
V+
V-
U1
AD8041
3
2
6
7
4
8
BOB-3 pin 29
VR1
2K
1
3
2
+
C1
10uF Tantalum
BOB-3 pin 28
R3
390
BOB-3 pin 23
VIDEO MIX
Video Out
BOB-3 Version 3.4 Application Guide ~ Copyright © 2004 by Decade Engineering ~ Page 6
