19 Level Plus Host Communication Protocol
This section describes the communication protocol required to access LEVEL PLUS Tank
Monitoring System data from a remote EIA 232 or EIA 485 communication device.
Hardware Considerations
RS485 SYSTEM This system allows one host terminal (or computer) to
communicate with up to 19 LEVEL PlUS monitors over
a two wire balanced differential network. Signals RX, TX,
and shield ground are supported. Communication is
restricted to half duplex operation only and the host
device must provide local character echo, as the LEVEL
PLUS system does not.
RS232 SYSTEM This system allows one host terminal (or computer) to
communicate with only one LEVEL PlUS monitors over
a standard EIA 232 network. Signals RX, TX, RTS, CTS
and signal ground are supported. Communication is
restricted to half duplex operation only and the host
device must provide local character echo, as the LEVEL
PLUS system does not. The EIA 232 system can also be
connected to an 80 column printer for data logging
purposes. Printer buffer size must be 1000 bytes or
larger. Printer interfaces should use CTS signal input to
indicate printer buffer full conditions. The Level Plus
will not transmit when CTS is low. If the CTS line is
low for more than 5 seconds, the scheduled
transmission will be aborted.
The asynchronous data format is 10 bits defined as follows:
1. Programmable checksum function disabled -1 start bit, 7 data bits, 1
parity but (even) and 1 stop bit. (ASCII).
2. Programmable checksum function enabled -1 start bit, 8 data bits
(even parity) and 1 stop bit (MODBUS RTU).
NOTES:
See
Appendix B
for serial printer interfacing information.
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