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Protocol Description
RS 232 - RLINK
Adapter
- V1.1.0 -
Bestell-Nr / Order no. 9103-xxxx
Contents
1 ............................................................................................GENERAL RS 232 COMMUNICATIONS PROTOCOL
2................................ TRANSMISSION OF COMMANDS TO DEVICES USING THE GENERAL PROTOCOL
3 ................................................RETURN TRANSMISSION FROM DEVICES (STATUS TRANSMISSION)
2
1 General RS 232 communications protocol
The basic structure of a command between an RS232 device and the RS232 adapter is as follows:
Address
Number of
data bytes
(0x00..0x0F)
(0x01)
Data byte 1
...
Data byte N
(flag byte)
Address:
The RS232 adapter has the fixed address 0x01
No. of data bytes:
Number of subsequent data bytes (max. 16)
(including the flag byte)
Flag byte:
Last data byte
for use with a Crestron device: 02 (hex)
Checksum:
The lowest-value byte (low byte) of the sum of all preceding bytes
(“address”, “No. of data bytes”, “flag byte” and data bytes)
Checksum
If a valid command is received from the adapter (i.e. the received and calculated checksums agree), an
Acknowledge signal is sent back to the control unit as confirmation. This Acknowledge has the following
format:
Address
(0x01)
Checksum
Checksum: the checksum of the received command is used as the checksum!
3
2 Transmission of commands to devices using the general protocol
The actual control command of a device is implemented as data bytes in the general structure:
0x01
Number of
data bytes
Data byte 1
...
device
address
command
Flag byte Checksum
...
Device address: (C8 hex) This is a specific device address which permits the transmission of control
commands
Command:
Control command (see Section 5.1)
Here is an example:
Transmission to K6
Command: Volume 0x01
0x03
Adapter address
Length
0xC8
device
address
C8 (hex)
0x20
0x02
command
(Volume-)
Flag byte
0xEE
Checksum
As already described in Section 2, the adapter sends back an Acknowledge sequence if a valid command is
transmitted; the complete transmission therefore takes the following form:
Command: Volume 0x01
0x03
0xC8
0x20
0x02
0xEE
Acknowledge (from Adapter after 30-40ms):
0x01
0xEE
Adapter address Checksum
If the command cannot be fed to the addressed device, a ‘Not Acknowledge’ sequence will be sent back by
the adapter. There are two possible replies:
NACK (from Adapter after 30-40ms):
0x01
0xED
adapter addr. checksum –1
0x01
adapter addr.
0xEC
checksum -2
The R-Link Bus cannot be serviced by the adapter
possible reasons: the R-Link cable is not connected,
master device is not powered up
The adapter can communicate with the master device,
but the addressed device doesn’t answer.
possible reason: the addressed device is busy
4
3 Return transmission from devices (status transmission)
Commands are available which cause a device status signal to be sent back in order to receive information
about the current status of a device.
This transmission also occurs within the framework of the general communications protocol, although the
data byte usage differs slightly from the transmission protocol.
0x01
Number of
bytes
Data byte 1
...
device com.
address
C4 (hex). echo
DB1
Flag byte Checksum
DB2
...
Device address:
(C4 hex) This is a -specific device address which grants access to the status
register!
Command echo:
The query command is repeated at this point
DB1, DB2,... :
Current status information (varies according to queried status)
Example:
Command: query amplifier status
0x01
0x03
0xC4
0x64
0xC4
Address echo
0x64
Command echo
0x02
0x2E
Acknowledge (from Adapter):
0x01
0x2E
Adapter address Checksum
Answer (via Adapter):
0x01
0x05
Required acknowledge:
0x01
0x...
Adapter address Checksum
DB1
DB2
DB3
0x...
Status bytes
Checksum
elektroakustik GmbH & Co. KG
Herford
Deutschland * Germany
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