Measurement Computing Extender488 - Manual (Page 12)

Section 2 Getting Started
2. 2
2.2 Extender488 CONFIGURATION
The following describes the configuration necessary for the RS-422 Extender488s. If you are using
the fiber optic extenders, refer to Section 2.3.
Two Extender488s are required to accomplish bus extension, with one c onnected directly to the
LOCAL IEEE bus, and the other connected to the REMOTE IEEE bus.
Both local and remote extenders are identical. At power up, each extender monitors the Attention
(ATN) and Remote Enable (REN) lines. The Error LED on each extender will blink indicating that ATN or
REN has not yet been detected and that communication with the other extender has not yet been
established. The first extender to detect either of these lines asserted declares itself the
LOCAL extender
and commands the other extender to declare itself the REMOTE extender. The Error LEDs will now stop
blinking. From this moment on, the LOCAL extender will monitor all local bus activity and transmit this
activity to the REMOTE extender. All activity detected by the REMOTE extender is also communicated
back to the LOCAL extender.
2.2.1 Extender488 Serial Baud Rate Selection
The Extender488 is shipped with the serial baud rate set to 115.2K baud. For most
applications, this is the most efficient operating rate. However, if the extenders are to be located at
extreme distances from each other, baud rates other than 115.2K can be selected. Selectable bau d
rates include 115.2K, 19.2K, 9600, 4800, 2400, 1200, 600, 300. Both extenders must be set to the
same baud rate for proper operation.
To modify the baud rate, follow this simple procedure: Disconnect the power supply from
the AC line and from the interface. Disconnect any IEEE or serial cables prior to disassembly.