VideoReQuest Protocol Guide v1.1.2 - 5/18/04
Phone (518) 899-1254
•
Fax (518) 899-1251
•
www.request.com
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5 -
Flags:
The 2 flag bytes are used to tell the VideoReQuest whether you do or do not want to use
certain features. Setting both to 00
h
turns off all options. Each byte is broken up into 8 bits.
Each bit is a flag for a certain feature. The possible options are as follows:
Byte 1
Byte 2
Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
ACK
Chk
Sum
Example:
To turn on the use of Check Sums, but not Acknowledgments, send
00h
,
01h
for the flag
bytes. This should be done on initialization of the connection as well as for any subsequent
command sent.
Data Size:
2 byte value that contains the length (in bytes) of the data portion of the command string.
For
Command Subtypes
1, 2,
or
3
, use the
Subtype
table on page 4 to determine the data
length. For
Command Subtype
4
, the following example illustrates how to calculate the
Data Size
:
Assume the length of the string is 25 bytes (25 characters, including spaces and
punctuation). This means that the full
Data Size
is 25 bytes PLUS 3 bytes for the
Engine, Mode,
and
Checksum
, or 28 bytes total.
BYTE 1
=
= 0, or 00
h
BYTE 2
=
28 MOD 255
= 28, or 1C
h
Header Check Sum:
If you are not using Check Sum (based on your Flag settings), then set this byte to
00
h
.
Otherwise, see
Calculating Checksum
on page 6 for more information.
Engine:
The Engine is simply the page that the VideoReQuest is currently on. Setting the Engine byte
to
FF
h
sends the command to whatever the current Engine is. Setting the Engine byte to a
specific engine (see table) sends the command to that engine ONLY.
Engine
Description
00
h
Sends command to Browse mode
01
h
Sends command to Player mode
02
h
Sends command to DVD player
FF
h
Sends command to default (current) engine
Mode:
The Mode is reserved for future use, and should always be set to
FF
h
.
Data:
These byte(s) are the actual command and possible arguments that you are sending to the
VideoReQuest. See
Data Commands
on the next page for a complete list of commands.
255
28