Lakeshore 425 - Chapter 6: Computer Interface Operation; 6.2 USB Interface

6.1 Ge n e r a l 45
| www.lakeshore.com
Chapter 6: Computer Interface
Operation
6.1 General
This chapter provides operational instructions for the computer interface for the
Lake Shore Model 425 gaussmeter. The computer interface provided with the
Model 425 permits remote operation; its commands are detailed in section 6.3.
6.2 USB Interface
The Model 425 USB interface provides a convenient way to connect to most modern
computers, as a USB interface is provided on nearly all new PCs as of the writing of
this manual. The USB interface is implemented as a virtual serial communication 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.
6.2.1 Physical
Connection
The Model 425 has a B-type USB connector on the rear panel. This is the standard
connector used on USB peripheral devices, and it allows a common USB A-type to
B-type cable to be used to connect the Model 425 to a host PC. The pin assignments
for A-type and B-type connectors are shown in section 8.7. 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 maximum total
length of 30 m (98.4 ft).
6.2.2 Hardware
Support
The USB interface emulates an RS-232 serial port at a fixed baud rate of 57,600, but
with the physical connections of a USB. This programming interface requires a cer-
tain configuration to communicate properly with the Model 425. The proper configu-
ration parameters are listed in TABLE 6-1.
The Model 425 hardware connection uses the USB 2.0 12,000,000 bits/s signaling
rate; however, since the interface uses a virtual serial communication port at a fixed
data rate, the data throughput is still limited to a baud rate of 57,600.
Baud rate 57,600
Data bits 7
Start bits 1
Stop bits 1
Parity Odd
Flow control None
Handshaking None
TABLE 6-1 Host communication port
configuration