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6.1 Structure of message
The messages consists out of a RCS-independent and a RCS-dependent layer. The RCS-independent
parts are interpreted the same by all types of devices. The
RCS-dependent parts contain specific com-
mands for a certain type of
RCM: the message body.
A message has the following structure:
<STX> <TYPE> <ADDRH> <ADDRL> <Body> <CHKH> <CHKL> <ETX>
These are the elements of a message in detail:
STX The control character STX (Ctrl-B) is the beginning of a
message. All previously received characters are ignored and
are not sent on. (Ctrl-B is displayed as in most terminal
applications.)
<TYPE> 1 byte ASCII
upper case class code to specify broadcast addressing.
<ADDRH><ADDRL> 2 bytes ASCII decimal
in broadcast addressing it is always 00
<Body> type-dependent part of the message, e. g. a command
<CHKH><CHKL> 2 bytes ASCII decimal
is the sum over all fields from <TYPE> to <Body>. The
checksum is evaluated by the recipient.
ETX The control character ETX (Ctrl-C)is the end of a message.
(Ctrl-C is displayed as in most terminal applications.)
Table 6-1
6.2 Processing a command in broadcast mode
As soon as an RCS recognizes that the command is sent in broadcast mode (e.g. in case of HERMES
DXD, the second character is an upper case M), it immediately starts passing the entire message to the
following
RCS. This ensures that all RCS of the Remote Control ring receive the command "at the same
time", thus being able to execute "simultaneously" the required action.
For broadcast commands, there is no acknowledge. However, the broadcast
message will loop back completed and unmodified to the RCM and may be
interpreted as acknowledge.