Larson Davis System 824, Reference Manual

Page: 401 / 536

9/12/00 B -3
Daisy Chain Addressing
The following instruments are com-
patible on a common network: Mod-
els 712, 720, 812, 814, 824, 870, and
TAC100. Future instruments may
also be compatible with this net-
work. A network of instruments may be interconnected to one
computer using the appropriate cabling, and each may be
controlled individually. Each is given a unique address. By
default, all 824s are given an address based on their serial
number from 1 to 100. Serial numbers that end with two
zeros will be addressed as 100. The addresses are sent as a
single byte ranging in value from 129 to 228 representing
address 1 to 100 respectively (address plus 128), while
addresses 101 through 127 are reserved. At power-on all
824s are address enabled (as if they had just received their
address). Whenever an address byte is received, only the
corresponding instrument is enabled to receive and respond
to commands.
A broadcast command can be sent. By sending an address of
zero, CHR$(128), all units on the chain will become
addressed and accept the commands that follow. Only the
device with an address of 1 will respond to the commands.
This will allow all units to be started at the same moment, or
to have the same setting sent to all devices with one com-
mand, i.e. set all clocks to the current time.
824 Network, Addressing Commands
NOTE: Hexidecimal notation: The dol-
lar symbol “$” is used to indicate hex-
idecimal notation. Example: $1A is the
hexidecimal notation for the decimal
value of 26.
The addressing of multiple 824s on a RS-422 network has
been enhanced so as to allow binary data blocks to be sent to
the 824 (and not be interpreted as an address), to automati-
cally identify all 824s on the network, and to control the
baud rate from the computer more easily. The command
details follow: