Interface

Connector

Physical layer

Rate

Protocol

USB

J4, USB-B receptacle (front panel “USB”)

USB 2.0 full speed, HID class

12 Mbit/s

Commander commands through the Commander HID API (no driver installation)

RS-485

J2, 3-pin 3.81 mm (front panel “RS485”)

2-wire, half duplex

9,600, 19,200, 38,400, 57,600, 115,200 baud

Commander ASCII commands

Command format

Commands are ASCII text. Over RS-485 each command is addressed to a device ID and terminated with a carriage return, and the controller replies with the requested value, OK, or ? for an invalid command. Over USB the same commands are sent through the Commander HID API (Windows DLL). See the Commander command reference [3] for the syntax and command set.

USB (J4)

USB 2.0 full speed, HID class: no driver signature or installation is required. The data lines have ESD protection. USB does not power the board: logic power must be applied to J3 for USB communication.

RS-485 (J2)

Pin

Panel label

Signal

Function

1

+

485+

RS-485 non-inverting (A)

2

−

485−

RS-485 inverting (B)

3

G

GND

logic ground reference

Parameter

Value

Transceiver

3.3 V RS-485/RS-422 transceiver, half duplex

Bus voltage

−7 V to +12 V (common-mode range)

Termination

120 Ω AC termination (120 Ω in series with 1 nF) permanently fitted; not switchable

Fail-safe bias

none on the board; bias the bus at one node if required

Protection

10 Ω series resistors, TVS diodes on both lines

Isolation

none: referenced to logic ground