Holtgreven GSE-355 I.S. - Manual (Page 96)

87
The RS-485 multi-drop network option supports both half duplex (2- wire) and full duplex (4-wire) modes of operation.
The mode of operation is determined by setting jumpers 1–4 on the RS-485 option board.
Table 28: RS-485 Mode of Operation
J UMPER H ALF DUPLEX F ULL D UPLEX D ESCRIPTION
1 Installed Open
2 Installed Open
Selects half or full duplex
3 Installed on the
endpoints of the
network
Installed on the
endpoints of the
network
Termination resistor (R8 –
121 Ω )
4 Installed Open Receiver disabled when
transmitting (if installed)
S
ETUP
The Model 350/355 controller supports address recognition, which allows a single master device to communicate with
up to 250 distinct slave controllers. P250 must be enabled in order to gain access to P251. Enabling P250 by itself only
causes the RTS line to become a driver enable for the RS-485 network option. Changing the P251 address to a value of
4 – 254 enables the network address recognition receive feature (i.e. networking).
O
PERATION
When P251 is enabled by choosing a valid address, the Model 350/355 will ignore all data it receives until an
character is followed immediately by a character that matches the address defined by setup parameter P251. If these
two conditions are met then the Model 350/355 will process all subsequent data until the end of block character,
, is received, signaling the end of the transmission. The receive routine of the Model 350/355 then resets to look
for the character again.
The data packet format recognized by the Model 350/355 is defined as follows:
Refer to Table 12: ASCII / HEXADECIMAL CONVERSION CHART on page 57 for and ASCII
codes. The address is a single byte decimal value (4 – 254). The can be any information recognized by the
Model 350/355, including direct commands – such as a %p (Print). This would direct the addressed unit to send its
print transmission defined at P213 over the network.
If the received address character does not match P251 then all of the subsequent data is ignored until the
next start of packet character,, is received.
An address of 0 at P251 will cause the Model 350/355 to process all received data.
N
ETWORK
P
ROTOCOL
The protocol settings for the RS-485 network option board are the same as the protocol settings for RS-232. These
settings are found starting at parameter P200.
All devices connected to the network must have matching protocol settings.