Pololu Jrk USB - Manual (Page 27)

4. Using the Serial Interface
4.a. Serial Modes
The jrk has three different serial interfaces. First, it has the RX and TX lines. The jrk can send bytes on the TX line.
If the jrk is in serial input mode, the RX line can be used to receive non-inverted, TTL (0 – 5 V) serial bytes (
Section
4.b ). If the jrk is not in serial input mode, it can not receive bytes on RX because the line is used for analog voltage or
pulse width measurement. Secondly, the jrk shows up as two virtual serial ports on a computer if it is connected via
USB. One of these ports is called the Command Port and the other is called the TTL port. You can determine the
COM port numbers of these ports by looking in your computer’s Device Manager. See
Section 3.a for information.
The jrk can be configured to be in one of three basic serial modes:
USB Dual Port
The USB Dual Port serial mode.
In this mode, the Command Port can be used to send commands to the jrk and receive responses from it. The baud
rate you set in your terminal program when opening the Command Port is irrelevant. The TTL Port can be used to
send bytes on the TX line and (if the jrk is in serial input mode) receive bytes on the RX line. The baud rate you
set in your terminal program when opening the TTL Port determines the baud rate used to receive and send bytes on
RX and TX. This allows your computer to control the jrk and simultaneously use the RX and TX lines as a general
purpose serial port that can communicate with other types of TTL serial devices.
USB Chained
The USB Chained serial mode.
In this mode, the Command Port is used to both transmit bytes on the TX line and send commands to the jrk. The
jrk’s responses to those commands will be sent to the Command Port but not the TX line. If the input mode is serial,
bytes received on the RX line will be sent to the Command Port but will not be interpreted as command bytes by the
jrk. The baud rate you set in your terminal program when opening the Command Port determines the baud rate used
to receive and send bytes on RX and TX. The TTL Port is not used. This mode allows a single COM port on your
computer to control multiple jrks, or a jrk and other devices that have a compatible protocol.
Pololu Jrk USB Motor Controller User's Guide © 2001–2014 Pololu Corporation
4. Using the Serial Interface Page 27 of 45