User manual

Prologix GPIB-USB Controller User Manual
9/15/2009 6
GPIB instrument at the currently specified address (See ++addr command) to listen, and
passes along the received data.
When Read-After-Write feature is enabled (See ++auto command) Prologix GPIB-USB
Controller will addresses the instrument to talk after sending a command, in order to
read its response. All data received from instruments over GPIB is sent to host over
USB. Read-After-Write feature simplifies communication with instruments. You send
commands and read responses without consideration for low level GPIB protocol
details.
When Read-After-Write feature is not enabled Prologix GPIB-USB controller does not
automatically address the instrument to talk. You must use the ++read command to read
data.
Controller mode is used to remotely control instruments and to download screen plots
by sending plot commands from a host computer.
6.2. Device Mode
In Device mode, Prologix GPIB-USB Controller acts as another peripheral on the GPIB
bus. In this mode, the controller can act as a GPIB TALKER or GPIB LISTENER
only. Since Prologix GPIB-USB Controller is not the Controller-In-Charge while in this
mode, it expects to receive commands from a GPIB controller. When Device mode is
enabled Prologix GPIB-USB controller configures itself as a GPIB Listener. All data
received by the controller over the GPIB port is passed along to the USB port without
buffering.
All data received from the host over USB is buffered until the GPIB controller addresses
Prologix GPIB-USB controller to talk, at which time the buffered data is passed along to
the GPIB port. The controller can buffer only one command. A subsequent command
received over USB will overwrite the previously buffered one, if the previous one has
not yet been transmitted over GPIB.
Device mode is used to download screen plots from the instrument front panel for
rendering using plotter emulation software.
7. Data Transmission
In Controller and Device modes, characters received over USB port are aggregated in an
internal buffer and interpreted when a USB termination character – CR (ASCII 13) or
LF (ASCII 10) – is received. If CR, LF, ESC (ASCII 27), or ‘+’ (ASCII 43) characters are
part of USB data they must be escaped by preceding them with an ESC character. All
un-escaped LF, CR and ESC and ‘+’ characters in USB data are discarded.