Chapter 6, COMPUTER OPERATION
6-6
When USBTERM has been set to 1, the terminator bytes are, in the following order:
1) A null character (ASCII 0)
2) A byte representing the value of the Status Byte (table 6-1)
3) A byte representing the value of the Overload Byte (table 6-1)
In the case of commands that generate a single response, the controlling program
should send the null-terminated command string to the instrument and then read the
response bytes sent back from it until the null is detected. If USBTERM is set to 1
then two further bytes (the status and overload bytes) should also be read to complete
the transfer.
Commands that do not return data still always return the one or three terminator
bytes, allowing the controlling program to know that the command has been
implemented.
Data stored in the instrument’s curve buffer can be transferred in two ways. In the
ASCII mode, each value is terminated in a null character until the last value, which is
then terminated as above, whereas in the binary dump mode each data point occupies
two bytes, with the complete dump being terminated as above.
In either case it is necessary to know how much data will be transferred before
initiating the transfer, by sending the M (monitor) command and reading the
response. This is because in the ASCII dump mode the controlling program needs to
“count” each instance of a null character until all available points have been read,
while in the binary dump mode it needs to know exactly how many bytes to read,
since the data itself can contain null characters. Only by doing this can the program
be prevented from requesting more data from the USB endpoint than the lock-in has
actually sent.
6.4.04 Delimiters
Most response transmissions consist of one or two numbers (expressed as ASCII
text) followed by a response terminator. Where the response of the lock-in amplifier
consists of two numbers in succession, they are separated by a byte called a
delimiter. This delimiter can be one of several ASCII characters and is common to
all interfaces; it is set via the DD command.
6.5 Ethernet Operation
6.5.01 Introduction
The Ethernet interface in the instrument supports operation on 10-BaseT and
100-BaseT networks via straight through or crossover RJ45 patch cables. The
instrument includes a built-in web server allowing any browser to communicate with
it using http protocol, as well as support for direct communication via TCP/IP.
6.5.02 IP Address
The IP address of the instrument needs to be unique on the network to which it is
connected. Consult section 5.2 for a discussion of the various ways of ensuring that
this is the case.
6.5.03 Main Controls
When the instrument has a valid IP address the browser on a computer on the same
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