Digital Video Recorder
73
Appendix F – External Protocols
Message Format
<BOM><ID>:<Class>:<Code>[:Operands]:<Checksum>[EOM]
where:
Symbol
Value
Description
:
:
Field delimiter
@
Beginning of message (for command)
<BOM>
<
Beginning of message (for reply)
<ID>
00~99
Device ID
<Class>
DR
Device Class (“DR” for DVR systems)
<Code>
AA~zz
Op-code (see below)
<Operands>
Optional operands defined for each operation
00~99
Checksum (sum of ASCII codes before checksum
discarding overflow)
<Checksum
>
*
No checksum
[EOM]
^J^M
End of message (optional: only for convenience of users
using general terminal)
*All digits are in decimal format. Letters are case sensitive.
Control Flow
• Every transaction consists of one command and one reply.
• Characters transmitted before <BOM> are ignored.
• The format of operands is defined independently for each op-code.
• The <BOM> received before <Checksum> of previous message resets interpretation;
i.e., discards the previous message. EXCEPTION: in the case of text input, none of the
characters within the specified length has special interpretation.
Common Reply
Reply code
Reply data
Description
Ok
Er
0000~9999
Error: return error number
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