Chapter 6, COMPUTER OPERATION
6-5
Bit Status Byte Overload Byte
bit 0 command complete X(1) output overload
bit 1 invalid command Y(1) output overload
bit 2 command parameter error X(2) output overload
bit 3 reference unlock Y(2) output overload
bit 4 output overload - read CH1 output overload
overload byte to determine location
bit 5 new ADC values available CH2 output overload
after trigger
bit 6 input overload CH3 output overload
bit 7 data available CH4 output overload
Table 6-1, Status and Overload Byte Bit Definitions
6.4 USB Operation
6.4.01 Introduction
The USB interface in the instrument supports operation at both Full and High Speed
settings. It provides two bulk data transfer endpoints, with endpoint 1 being used to
send commands to the instrument, and endpoint 2 being used to receive responses
from it.
Operation of the instrument via the USB is made a great deal simpler if the user
installs the relevant SIGNAL RECOVERY USB driver software. Two versions of
driver are available; the first, a bulk USB driver SRUSBXP.SYS is compatible with
several software packages supplied by SIGNAL RECOVERY, while the second,
based on National Instrument’s VISA software, allows operation both from
SIGNAL RECOVERY software and a free LabVIEW driver. The only disadvantage
of using the VISA software driver is the need to download and install the complete
VISA environment in order to use the driver.
Readers should refer to the document “USB Drivers for the Model 7124, 7230, and
7270 Lock-in Amplifiers”, available from the www.signalrecovery.com website, for
further information about installing these drivers.
6.4.02 General Features
Unlike the RS232 interface, there is no difficulty ensuring that the correct cable type
is used for USB operation. All that is required is a standard USB-A to USB-B cable,
which if the driver is correctly installed on the computer will then allow operation
without further adjustment.
6.4.03 Terminator, Status Byte, and Overload Byte
Commands sent to the instrument over the USB interface should be terminated with
a null character (ASCII 0).
Responses from the instrument consist of a string that is terminated with either one
or three bytes, depending on the setting specified by the USBTERM command – see
section 6.7.11
When USBTERM has been set to 0, the terminator is:
1) A null character (ASCII 0)
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