Lake Shore Cryotronics 121, User Manual

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Chapter 4: Computer Interface
Operation
4.1 General
This chapter provides operational instructions for the computer inter-
face for the Lake Shore Model 121 Current Source. The Model 121 pro-
vides a USB interface described in section 4.2. The Model 121 permits
remote operation through the USB interface. The interface commands
are detailed in section 4.3.
4.2 USB Interface
The Model 121 USB interface provides a convenient way to connect to
most modern computers. The USB interface is implemented as a virtual
serial com port connection. This implementation provides a simple
migration path for modifying existing RS-232 based remote interface
software. It also provides a simpler means of communicating than a
standard USB implementation.
4.2.1 Physical Connection
The Model 121 has a B-type USB connector on the rear panel. This is the
standard connector used on USB peripheral devices, and it allows the
common USB A-type to B-type cable to be used to connect the
Model 121 to a host PC. The pin assignments for A-type and B-type con-
nectors are shown in section 6.7. The maximum length of a USB cable, as
defined by the USB 2.0 standard, is 5 m (16.4 ft). This length can be
extended using USB hubs every 5 m (16.4 ft) up to 5 times, for a maxi-
mum total length of 30 m (98.4 ft).
4.2.2 Hardware Support
The USB interface emulates an RS-232 serial port at a fixed 57,600 baud
rate, but with the physical connections of a USB. This programming
interface requires a certain configuration to communicate properly with
the Model 121. The proper configuration parameters are listed in
TABLE 4-1.