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4.2.3 Structure of Messages
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
declares the type of class of addressed RCS.
<ADDRH><ADDRL> 2 bytes ASCII decimal
addresses the n-th RCS within a class of the specified type.
<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 4-2
Four different types of messages are used:
commands RCM sends command messages to a RCS.
acknowledge RCS sends responses to the RCM after having executed the command
responses RCS sends responses to the RCM on request.
interrupts RCS reports errors to the RCM without request.
Table 4-3
4.2.4 Acknowledge
The acknowledge is composed of the command the RCS has received and executed and the internal
Status Register.
An acknowledge has the following structure:
<STX><TYPE><ADDRH><ADDRL><Body><STATH><STATL><CHKH> <CHKL><ETX>
These are the elements of an acknowledge 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
declares the type of class of addressed RCS.
<ADDRH><ADDRL> 2 bytes ASCII decimal
addresses the n-th RCS within a class of the specified type.
<Body> type-dependent part of the message, e. g. a command
<STATH><STATL> 2 bytes Hexa decimal
information about the internal Status Register
<CHKH><CHKL> 2 bytes ASCII decimal
is the sum over all fields from <TYPE> to <STATL>. The checksum
is evaluated by the Remote Control Master.
ETX The control character ETX (Ctrl-C)is the end of a message. (Ctrl-
C is displayed as in most terminal applications.)