Symmetricom 5071A, Operating And Programming Manual

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Chapter 4 Remote Operation and Programming
Tips on Using the RS-232C Port on the 5071A
Operating and Programming Manual 65
Tips on Using the RS-232C Port on the 5071A
The RS-232C port on the 5071A rear panel is very useful for controlling the
instrument and gathering data. However, communication via the RS-232C is not
always a connect-and-go process. Until recently, there were many different
vendors producing differing handshaking protocols, data rates, and wiring
connections.
Because of the myriad of possible hardware, system, and software combinations,
there are many ways to incorrectly set up and connect the RS-232C and
potentially lock-up the system. This condition usually appears as non-sensible
characters being received, or no communication at all.
This section is intended to give you a summary of how some RS-232C lock-ups
occur and how best to clear them.
Keypad Lock-Ups
: Why do they occur and how are they cleared?
Description
First, make sure the padlock symbol does not appear in the LCD display. If so,
the 5071A is locked via the SCPI command SYST:REM ON and must be
unlocked before some front panel operations can be accepted. Refer to this
manual for instructions on how to unlock the front panel.
If this is not the case, the 5071A front panel can appear to be frozen (no key
presses accepted) if it is communicating with another serial device via the RS-
232C and receives a data holdoff from that device. There are two types of
holdoffs: One is the XON/XOFF (software) protocol, and the other is the DSR
(Data Set Ready) line (hardware). Either of these can be used by printers or
terminals. The 5071A is capable of understanding both.
XON/XOFF
When a connected terminal or printer uses the XON/XOFF protocol the 5071A
will hold off further data transmission when an XOFF (Control-S) is received.
This usually happens when a terminal/printer buffer is full or if a printer is out of
paper.