Communicating With The Videorequest; Sending Commands; Breakdown Of Each Command Portion; Marker - ReQuest Multimedia VideoReQuest Protocol Manual

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:

Marker

Command
Type
FCh A0h 0Ah

Breakdown of Each Command Portion:

Marker:
The Marker bytes are ALWAYS FCh, A0h. These bytes tell the VideoReQuest the data that
follows is valid.

Command Type:

The Command Type will almost always be 0Ah when sending commands to the
VideoReQuest. All possible command types are as follows:
Command
Type
05h
0Ah
0Fh
14h
19h

Command Subtype:

The 4 possible subtypes are as follows:
Command
Subtype
01h
02h
03h
04h
* The data length includes the Engine, Mode, and Data Checksum bytes.
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HEADER
Command Flags
Subtype
1 Byte 00h 00h
Description
Start Communications (see Initializing the Connection
on page 6 for more information
Command (most commands sent to the VRQ)
Data (not typically used)
Acknowledgement (used only if ACK flag is turned ON)
End Communications (used to terminate connection)
Description
1 byte command, no arguments
2 bytes (1 for command, 1 for character argument)
5 bytes (1 for command, 4 for integer argument)
Multi-byte string argument
VideoReQuest Protocol Guide v1.1.2 - 5/18/04
Data Size Chk
Sum
Byte 1 Byte 2 00h
www.request.com
4 -
-
DATA
Engine Mode Data
FFh FFh 1+ Bytes
Data Length
(bytes)*
4
5
8
TBD
Chk
Sum
00h