Network Programmingof Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE)
(www.ashrae.com).- BITBUS. Introduced by Intel. General-purpose primary/secondary proto-
col. BITBUS European Users Group (www.bitbus.org) has documentation.
An expanded version is defined by the withdrawn IEEE Standard
1118-1990. - CTNet. Features de-centralized control and high performance (www.con-
troltechniques.com). - INTERBUS. Used in automotive applications. Promoted by the INTER-
BUS Club (www.interbusclub.com). - Modbus. Developed by Modicon and now an open standard. Modbus RTU
transmits binary data. Modbus ASCII transmits text data. Promoted by
Modbus-IDA (www.modbus.org) - PROFIBUS (Process Fieldbus). Used in manufacturing, process control, and
building automation. From Profibus International (www.profibus.org). - SAE J1708. For vehicle applications. From the Society of Automotive Engi-
neers (www.sae.org).
High Tech Horizon (www.hth.com) offers the free, generic S.N.A.P. protocol.
Some data-acquisition devices support vendor-specific ASCII command sets.
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Because of their complexity, networks can be challenging to debug. A gradual
and deliberate approach to putting together or debugging a network can save
time in the long run. These are some techniques that can be useful:
Start with two nodes. In a primary/secondary network, connect the primary
node to one secondary node and get that working before adding more nodes.
Keep the distance short. If possible, place the nodes in the same room,
side-by-side, until things are working.
Use a slow bit rate. A slow bit rate is especially useful if your debugging tools
are limited. At 300 bps, you can watch LEDs flicker on a breakout box when a
node transmits.
Use your programming environment’s debugging capabilities. Breakpoints,
watch variables, single-stepping, and other debugging tools can help isolate the
source of problems.
Monitor the network traffic. As with RS-232, a digital oscilloscope or logic
analyzer can help by showing exactly what’s happening on the line. Many