Measurement Specialties 9116 - Manual (Page 27)

Pressure Systems, Inc. Model 9116 User’s Manual
Page 18 www.PressureSystems.com
Chapter 3
Programming and Operation
3.1 Commands & Responses
3.1.1 Introduction
This chapter describes all commands a host computer program may send to a Model 9116
Intelligent Pressure Scanner module, as well as the data or status responses returned by the
module. Most applications require a working knowledge of only a small number of these
commands.
Model 9116 has an Ethernet interface, and uses layered TCP/IP or UDP/IP transmission
protocols to communicate with a host computer. All commands/responses to/from Model 9116
modules are embedded in the data fields of either a TCP or UDP packet header. In turn, these
packets are themselves embedded in the data field of an IP packet header, which is embedded
in the data field of an Ethernet packet header. Thus, the term layered protocols.
3.1.1.1
TCP/UDP/IP Protocols
Both TCP/IP and UDP/IP protocols are a well-established set of rules for communicating over a
network (LAN, intranet, or internet), and are independent of the network’s physical medium. All
the modules use the TCP/IP protocols for most commands and responses since the TCP layer
provides a robust error detection and correction mechanism. TCP/IP requires a formal
connection be established between host and module. The simpler UDP layer, requiring no
formal connection, is utilized for a subset of commands and query responses.
Using the underlying basic IP protocol, the host computer and interconnected modules are all
“peers” that can communicate equally. Each “peer” must have its own unique “logical” IP
Address (as well as its own unique “physical” Ethernet Address) to be directly addressed. Any
“peer” may initiate transmissions without permission from the receiver. In the NetScanner
™
System implementation, the host computer is normally a client and generally initiates most
transmissions by sending commands to the modules, which are normally servers. However, a
module can initiate its own transmissions in some operating modes (e.g., the hardware-
triggered or free-run autonomous host streams generated by the Configure/Control
Autonomous Host Streams (‘c’) command).
A “peer” may be directly addressed by its IP address (in xxx.xxx.xxx.xxx format), or by use of a
predefined logical name that allows its IP Address to be looked-up in the sender’s database or
in a central network server’s database. The Windows
® 95/98/XP/NT operating systems provide
a simple text file database called “Hosts.” Review the file “Hosts.sam” in the “C:\windows”
directory. Modify and rename it “Hosts.” (no file extension) to activate it.
Before the host computer and any module can communicate with the higher level TCP/IP
protocols, the host (client) must request a connection be established with the module (server).
Each module expects all such requests for connection to be requested by its IP Address, and