California Instruments 2001RP, User And Programming Manual

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User and Programming Manual - Rev N
8.6 Trouble Shooting - RS232C
This section provides guidelines for resolving communication problems that may occur when
using the PGUI32 software under Windows
™
.
You may encounter problems when using the serial interface with the PGUI32 program that is
supplied with the interface option for this source.
Symptoms:
1. Unable to verify connection to the power source through RS232C interface. Time-out occurs
and dialog box appears that asks if you want to switch to simulation mode. An error
message (ERR -100) may appear on the front panel LCD’s of the power source.
- Or -
2. Verification is successful but slewing of voltage, frequency or current limit results in an ERR
-100.
Things to check first:
1. Is the PC com port you selected to use really available for this purpose? On older PC’s com
port interrupts are often shared between com 1 and com3 as well as com2 and com 4. If any
of these other com ports is in use, it may prevent you from using the com port that shares
the same interrupt.
2. Did you use the RS232C cable that was supplied with the P/RP AC source? This is not a
null-modem cable and cannot easily be obtained at a computer store. If you do not have the
original cable, consult the PGUI32 on line help under Interface settings for a wiring diagram.
3. Did you connect the cable in the right direction? This cable is uni-directional and should be
marked with a SOURCE and a PC label. Make sure you connect the SOURCE side of the
cable to the back of the AC source and the PC side of the cable to the PC port.
Resolution for Symptom 1
The P and RP Series of AC sources require hardware handshaking to control data flow from the
PC to the AC source. After receiving a command, the AC source asserts the DTR line to hold off
further communication from the PC until the command just sent has been processed. Under
Windows 95, it is possible to use a 16 byte transmit buffer if a 16550 UART is present. This
FIFO exceeds the length of most AC source commands. When enabled, this mode may result in
more than one command being placed in the UART output buffer. If this happens, the
handshake from the AC source will not prevent the content of this buffer being sent to the AC
source and thus will result in more than one command being sent to the AC source.
To resolve this problem, the UART FIFO length needs to be reduced or disabled altogether. The
procedure to disabled the FIFO mode is outlined in the next paragraph.
Note: If turning off the UART FIFO conflicts with other applications that need to run on the same
PC using the same COM port, this solution may not be acceptable. In this case, skip this step
and proceed to the second symptom resolution which relies on a software implemented hold-off
instead of turning off the FIFO buffer. If you are using Windows 3.1 and experience the same
problem, the latter method is the only resolution available to you so you should skip the next
paragraph as well.
2001RP April 2007 67