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IEEE 488 Introduction
IEC 625
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BS6146
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NOTE: Never, ever connect an IEC 625 system to an
RS232C system. The =/- 12 Volts of the RS232C system can
seriously damage the 5 Volt TTL IEC 625 system!
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IEEE 488-1975.
The full name of the IEEE Standard 488-1975 is "A
Digital Interface for Programmable Instrumentation". It defines a
byte serial bit parallel interface for instrument systems. What
does this mean?
By Digital Interface it means that the signal on any of the
16 signal lines is either high or low. The voltage on each line
represents the On or Off state. So the data exchanged between
the devices connected together is digital.
Bit Parallel means that 8 lines are used to simultaneously
transmit a whole byte of data. These 8 lines are called
collectively the Data Bus. The data on the bus ranges in value
from 0 to 255. Since data is sent 8 bits at a time the IEEE bus
is inherently faster than the one bit at time RS232 system.
Byte Serial means that consecutive bytes of data are sent
one after another. Another example of bit parallel byte serial
data transfer is the Centronics Parallel printer connection found
on most PC's.
Programmable Instrumentation means that the devices
attached to the IEEE bus are usually capable of being instructed
to perform several different tasks in a sequence. Often an IEEE
system comprises devices that can measure various parameters
and devices that can generate various stumulii. For example a
programmable IEEE voltage generator may be instructed to apply
several voltages across a resistor, whilst a programmable IEEE
Ammeter may be used to measure the current through the
Chapter 2
This European standard is identical to the IEEE
standard except for the connector. It uses a 25
pin D type RS232C style connector.
This British standard is identical to IEC 625
PSI BOX Reference
Page 11
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