VideoReQuest Protocol Guide v1.1.2 - 5/18/04
Phone (518) 899-1254
•
Fax (518) 899-1251
•
www.request.com
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4 -
C o m m u n i c a t i n g w i t h t h e V i d e o R e Q u e s t
Before you can communicate with the VideoReQuest, you must initialize the connection. A
“Start Communications” command is similar to all other commands, with a few exceptions.
See
Initializing the Connection
on page 6 for more information.
S e n d i n g C o m m a n d s
Commands are sent to the VideoReQuest in strings of Hexadecimal (or Hex) numbers.
Depending on the command, these strings are anywhere from 13 bytes to 17 or more bytes.
All commands are in the following format:
HEADER DATA
Marker
Command
Type
Command
Subtype
Flags
Data Size
Chk
Sum
Engine
Mode
Data
Chk
Sum
FC
h
A0
h
0A
h
1
Byte
00
h
00
h
Byte 1
Byte 2
00
h
FF
h
FF
h
1+ Bytes
00
h
Breakdown of Each Command Portion:
Marker:
The
Marker
bytes are ALWAYS
FC
h
,
A0
h
. These bytes tell the VideoReQuest the data that
follows is valid.
Command Type:
The
Command Type
will almost always be
0A
h
when sending commands to the
VideoReQuest. All possible command types are as follows:
Command
Type
Description
05
h
Start Communications (see
Initializing the Connection
on page 6 for more information
0A
h
Command (most commands sent to the VRQ)
0F
h
Data (not typically used)
14
h
Acknowledgement (used only if ACK flag is turned ON)
19
h
End Communications (used to terminate connection)
Command Subtype:
The 4 possible subtypes are as follows:
Command
Subtype
Description
Data Length
(bytes)*
01
h
1 byte command, no arguments
4
02
h
2 bytes (1 for command, 1 for character argument)
5
03
h
5 bytes (1 for command, 4 for integer argument)
8
04
h
Multi-byte string argument
TBD
*
The data length includes the
Engine
,
Mode
, and
Data Checksum
bytes.
