Issue
112 November 1999
Tuning
into the HA Channel
Getting
to Know BOB
The
BOB-II module packs a lot of functionality on a tiny
SIMM circuit board. Photo 1 shows the Bob-II installed
in the PIC-TV circuit board. The bulk of the video work
is done by the SGS-Thomson STV5730A chip.
Using
internal registers, the chip is controlled by an external
microcontroller. The STV5730A also allows various configurations
to be used for whatever application you have. Give the
datasheet a read to see how this thing ticks. It’s
quite impressive.
On
the BOB-II, an Atmel processor handles all the STV5730A
control and external system communications. By using
a 9600-bps serial interface, you can send various control
commands (as well as normal text) to the BOB-II.
To
make the BOB-II appealing to a wide market, the command
set is RISC-like, simple, and straightforward. However,
you can combine commands to make a more powerful interface.
Table 1 shows the BOB-II command set. As you can see,
it enables you to control most of the STV5730A functionality.
| Table
1—The BOB-II command set is compact making
it ideal for machine to machine communication. There
are no cursor control commands except for moving
to a specific set of coordinates. Any other cursor
control must be handled by a host processor (i.e.,
the PIC-TV). |
Most
commands are preceded by a { and consist of a command
letter and sometimes a setting number or row, column
pair. The compact command set ensures that you don’t
waste time sending long command names over the 9600-bps
communications link and makes it easy to implement a
more detailed command set on the HCS interface processor.
A
number of normal characters like &, (,), %, and
! are absent from the BOB-II character set. Instead,
many foreign-language characters are used, which makes
the system more versatile.
It’s
clear why certain symbols were left off. The STV5730A
chip is intended for use in self-contained devices like
VCRs which don’t use % and the like.
However,
there are some neat symbols for use in a home automation
system. There are arrows, blocks for graphing absolute
values, and other video-related symbols.
Notice
the character codes don’t correspond to ASCII codes.
If you send normal text in ASCII, the BOB-II converts
it to the proper character code. However, if you want
to use the special character function to select characters
by byte codes, you must use the BOB-II character code.
