BOB-3 Version 3.4 Application Guide ~ Copyright © 2004 by Decade Engineering ~ Page 2
Video Modes
This document makes references to the video operating modes offered by BOB-3. The basic modes are “Local”
and “Genlock”. Genlock mode may also be called
overlay
mode, because video generator synchronization
(genlock) must be achieved in order to superimpose characters on the image. A third video operating mode,
“Automatic,” derives from BOB-3’s ability to switch between the basic modes by detecting video input.
BOB-3 powers up in Automatic. If there’s no video input, it selects local mode. In this case, BOB-3 generates the
complete video signal, and characters appear on a blue (by default) matte background. If video input is present,
BOB-3 switches to genlock mode so that characters are superimposed on the externally generated video signal.
BOB-3 continues to monitor incoming video and switch between the basic modes as required to maintain a video
signal at the output.
Application programmers can force BOB-3 to stay in local or genlock modes if desired. Be aware, however, that
video crosstalk artifacts can result from forcing local mode while video input is applied. Undesired mode switching
(to local mode) due to incoming video signal dropouts or glitches can be avoided by forcing genlock mode. BOB-3
exhibits better behavior than BOB-II in this respect, so it’s unlikely that you will be compelled to deal with video
mode control directly.
Specifications
Physical
BOB-3 is designed in the 30-pin SIMM form factor, 3.50 x 1.05 x 0.35 inches. Module weight is about
0.42 ounces (12 grams). Ambient operating temperature range is 0~50 degrees C.
Power
Supply
Nominal supply voltage range is +5VDC ±5% or +8~15V at 70mA typical. An aux5V regulated
output (pin 3) is rated at 50mA and ±5% voltage tolerance. Auxiliary supply output current adds to
main supply current drain, when main supply input (pin 1) is used.
Data I/O
The data path is asynchronous serial with crystal-controlled rates of 1200, 2400, 4800, 9600, 19.2K,
38.4K, 76.8K, and 153.6K bits/S, using 8 data bits, no parity, one stop bit (8N1), and inverted data.
Maximum low logic input level: 1.0V. Minimum high logic input level: 3.0V. Default bit rate is 9600. Bit
rates are selectable via pin strapping–see Pin Descriptions. BOB-3 connects directly to the UART
TXD/RXD pins of most microcontrollers. An inverting RS-232 interface (industry standard) is required
for connection to PC COM ports. Software handshaking is provided, but use is not mandatory. Six
pins serve as software-controlled digital outputs.
Speed
Printable characters are normally written to display RAM within a few uS after the stop bit is
received, so total print delay time is essentially that of the serial interface (e.g. 521uS per character
at 19,200bps). Characters may not appear in the display until the next video scan cycle, depending
on when they are written. If single-frame print timing accuracy is required, host write cycles should
be triggered from vertical sync. The crawl mode supplemental circuit given in this document is a
vertical sync separator, and it’s often suitable for this purpose.
Video I/O
BOB-3's video environment is RS-170A (NTSC) composite baseband, 1Vpp 75 ohms unbalanced.
PAL-B video compatibility is available as an ordering option. Y/C video (S-Video) can be
accommodated with external circuitry. The video input accommodates up to +2.5VDC bias mixed
with incoming video. The video output contains a small DC bias (+1V), which is common to many
video sources and is well tolerated at the inputs to most video equipment. An internal color video
background signal is automatically generated if video input is not supplied, but application programs
may enforce genlock or local video modes. Video control and timing signals are available by
software command at six output pins.
Character
Format
Up to 680 characters may be displayed on screen, in 40 columns and 17 rows (16 if vertical scrolling
is active). 320 character patterns are provided as 12x13 pixel bitmaps, including upper & lower case,
italics, European language support, and a set of graphics characters useful for lines, bar graphs, etc.
Non-ASCII characters are accessible through a simple command protocol. 63 of the standard
character patterns are stored in font RAM and may be replaced by user-defined bitmaps, to support
character-based graphics displays or alternate languages.
