Specifications

Readback is Intermittently Corrupted or Empty
Question: Why is the readback from my power supply intermittently corrupted or empty?
Answer: This problem frequently occurs on the second of two queries. While this is most common with the 662xA
family of supplies, it can occur on other system power products, but generally only if they are being used in
compatible language mode. This may occur with a recent purchased supply while others of the same type which have
been in the system for some time operate satisfactorily.
This problem arises from an internal difference in GPIB chips from certain suppliers. The problem is that the newer
design GPIB chip may cause a line feed character to remain in the output buffer after the readback query. Normally,
the power product firmware will clear the leftover bit out of the buffer when it prepares a response to the next query.
However, if the second query comes in too quickly, the leftover “line feed” is returned and may appear as a null
string.
For a temporary workaround, make sure every query is terminated with a or EOI . Make sure that all characters in the
buffer are read back before initiating another query. To accomplish this, insert a wait statement of at least 200 ms
after any query before beginning to read back the characters.
For products which display this problem, there is a firmware fix that can be implemented at the Service Center.
Contact your local Sales Office or Call Center, for more information. Click on the "Assistance" button in the upper
left corner to obtain the number of the office nearest you.