EZT-570S User Communication Reference Manual
A.4
IEEE488 –
Bus developed by Hewlett-Packard in 1965 as HP-IB. Also referred to as GPIB (General
Purpose Interface Bus). Consists of 8 data lines and 8 control lines. Bus length limited to 20.0
meters. Supports 15 devices on the bus at one time.
Logic Level –
A voltage measurement system where only two stable voltage values exist. Example:
0v and 5V, or -3v and +3v.
Mark –
Represents the transmission of data bit logic 1 (see logic level). Usually this is the most
negative voltage value in serial communications.
Master –
The device on the bus that controls all communications. Only the master can initiate
conversation.
Modbus –
A software protocol developed by Gould Modicon (now AEG) for process control systems.
No hardware interface is defined. Modbus is accessed on the master/slave principle, the protocol
providing for one master and up to 247 slaves. Only the master can initiate a transaction. This is a
half-duplex protocol.
MMI –
Man to Machine Interface typically performed in software on a personal computer. Also called
HMI.
Network –
When two or more devices share communication lines, the devices are “networked”.
Node –
A point of interconnection to a network.
Noise Immunity –
The ability of communication lines to ignore electrical noise generated in the lines
by nearby magnetic and electrostatic fields.
Odd –
This term is used with parity. See parity.
Parallel –
Communication using this method, transfers eight bits or one byte at a time over eight data
wires and one ground wire. This method is eight times faster than using serial but utilizes more
hardware.
Parity –
A bit is assigned at the beginning of a byte to stand for parity. When the ‘1’ bits are counted,
the number will be even or odd. A parity bit is used to ensure that the answer is always even if even
parity or odd if odd parity. If the receiving end counts the ‘1’ bits and the sum is not the same odd or
even, an error is generated. Parity is used to detect errors caused by noise in data transmission.
Protocol –
A set of rules for communication. This will specify what method to transfer information,
packet size, information headers and who should talk when. It is used to coordinate communication
activity.
Receive –
To accept data sent from another device. The device that receives the data is the
receiver.
Register –
An area of memory that provides temporary storage of digital data.
RJ11 –
A connector used on most telephones that has four terminals.
