User and Programming Manual - Rev H
California Instruments
P Series
May 2000
43
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.
Procedure
1. Make sure the PGUI program is closed and no device is using the com port in use.
2. From the Windows 95 desktop, right click on the “My Computer” icon which is located in the top
left corner of the screen.
3. From the popup menu, select the “Properties” entry.
4. This brings up the System Properties dialog box
5. From the tabs shown at the top of the dialog box, select the “Device Manager” tab.
6. The relevant screen is shown in Figure 9-1
Figure 9-1:
System
Properties
Dialog Box