RS232 & GPIB INTERFACE
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CHAPTER 12 : RS232 & GPIB INTERFACE
This section provides information on the proper use and configuration of bus remote
interface. The GPIB (IEEE-488) remote interface is standard on model 510L but the RS-
232 interface option can be substituted for the GPIB interface. The RS-232 interface also
uses the same command list as the GPIB with the exception of the SRQ functions. Please
refer to the Option section of this manual for details on the 7611 options.
12.1 GPIB Messages
There are typically two types of messages that GPIB devices use to communicate
with other interconnected GPIB devices;
Interface messages
:
often called commands or command messages and Device
dependent messages often called data or data messages.
Data Messages
:
contain information such as programming instructions or
measurement results. Command Messages perform functions such as initializing
the bus and addressing and unaddressing devices.
12.2 Functions
A GPIB device can be a Listener, Talker and/or Controller. A Talker sends data
messages to one or more Listeners, which receive data. A Controller manages the
information flow on the GPIB by sending commands to all devices. The GPIB
bus is much like a computer bus except a computer has circuit cards connected via
a backplane and the GPIB has stand alone devices connected via a cable.
12.3 Signals and Lines
The GPIB consists of 16 signal lines and 8 ground-return or shield drain lines.
The 16 signal lines are grouped into 8 data lines, 3 handshake lines and 5 interface
management lines.
Data Lines: The eight data lines, DI01 through DI08 carry data and command
messages. The 7-bit ASCII or ISO code set is used and the eighth bit DI08 is unused.
Handshake Lines: The transfer of message bytes between devices is done via
three asynchronously control lines. Referred to as three-wire interlocked
handshake. This guarantees that message bytes on the data lines are sent and
received without transmission error.
NRFD
(not ready for data) indicates when a device is ready or not ready to
receive a message byte.
NDAC
(not data accepted) indicates when a device has or has not accepted a
message byte.
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