Genlock Overlay Generators ~ Product Comparison

Two Videotext Overlay Modules Compared

BOB-I is much larger and heavier than BOB-II, even allowing for the SIMM socket used with BOB-II.

BOB-II accepts ‘RS-232’ style asynchronous serial data at rates up to 19,200bps (in V1.2). The data path to BOB-I is synchronous serial (separate clock & data lines) at a much higher maximum rate—2.5Mbps. This implies that faster screen updates are possible with BOB-I. If your host is fast enough, BOB-I could rewrite all of its 240 characters in 1.6mS. BOB-II can rewrite an entire screen of 308 characters in about 160mS (at 19.2kbps). If you’re refreshing a moderate number of characters, either model is effectively "real-time."

Application programming is much simpler with BOB-II. From the programmer’s point of view, it resembles a simple serial printer. BOB-I looks like a set of control registers which must be managed at the individual bit level—it’s a typical ‘dumb peripheral’ device.

BOB-I can adjust its display position in single-pixel increments (the character display grid moves en masse). BOB-II is restricted to movement in increments of whole character cells.

BOB-I offers character size choices, including really HUGE characters. BOB-II has only one size, and it’s smaller than BOB-I’s smallest size, yielding 308 displayable characters for BOB-II versus 240 for BOB-I. BOB-II produces about the smallest size of characters that may be superimposed on composite video with high legibility.

BOB-I has a chroma PLL, so it can produce color in Genlock/Overlay mode. BOB-II produces only monochrome characters in this mode. Both models produce color in Local video mode.

BOB-II switches video modes automatically, based on the presence of video input. BOB-I must be controlled by the host, and the host may need an independent method of detecting video presence.

External character & background brightness control is possible with BOB-II only.

BOB-II is available for NTSC video (USA) or PAL video (export). BOB-I is available for NTSC only.

BOB-I has a differential video input circuit to reject common-mode noise (often found in industrial video systems), and a glitch-protected power input circuit. BOB-II has a conventional video input circuit and basic power supply filtering. Both models use on-board 5V regulator ICs, however.

Only BOB-II offers an output from its video sync separator, which may be handy if auxiliary video processing circuits are needed in your system.

The character sets are different. BOB-II has European language support and better symbols for making horizontal and vertical bar graphs. BOB-I can make better lines and frames.

Click BOB-I or BOB-II for full product descriptions.