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4.2.3 Structu re 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 Acknow ledge
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.)
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