Pololu Maestro - Manual (Page 46)

Daisy chaining serial devices that have a TXIN input.
Using a PC and a Maestro together as the master device
The Maestro can enable a personal computer to be the master device. The Maestro must be connected to a PC with
a USB cable and configured to be in either USB Dual Port or USB Chained serial mode. In USB Dual Port mode,
the Command Port on the PC is used for sending commands directly to the Maestro, and the TTL Port on the PC is
used to send commands to all of the slave devices. In the USB Chained mode, only the Command Port is used on the
PC to communicate with the Maestro and all of the slave devices. Select the mode that is most convenient for your
application or easiest to implement in your programming language.
Using a Maestro as a slave device
The Maestro can act as a slave device when configured to be in the UART serial mode. In this mode, commands are
received on the RX line, and responses are sent on the TX line. A USB connection to a PC is not required, though an
RX-only Comand Port is available on the PC for debugging or other purposes.
Connections
Connect the TX line of the master device to the RX lines of all of the slave devices. Commands sent by the master
will then be received by all slaves.
Receiving serial responses from one of the slave devices on the PC can be achieved by connecting the TX line of that
slave device to the RX line of the Maestro.
Receiving serial responses from multiple slave devices is more complicated. Each device should only transmit when
requested, so if each device is addressed separately, multiple devices will not transmit simultaneously. However, the
TX outputs are driven high when not sending data, so they cannot simply be wired together. Instead, you can use
an AND gate, as shown in the diagram, to combine the signals. Note that in many cases receiving responses is not
necessary, and the TX lines can be left unconnected.
Whenever connecting devices, remember to wire the grounds together, and ensure that each device
is properly powered. Unpowered devices with a TTL serial port can turn on or partially on, drawing
power from the serial line, which means that extra care must be taken when turning power off and on
to reset the devices.
Sending commands
The Pololu Protocol or Mini SSC protocol should be used when multiple Pololu devices are receiving the same serial
data. This allows the devices to be individually addressed, and it allows responses to be sent without collisions.
If the devices are configured to detect the baud rate, then when you issue your first Pololu Protocol command, the
devices can automatically detect the baud from the initial 0xAA byte.
Some older Pololu devices use 0x80 as an initial command byte. If you want to chain these together with devices
expecting 0xAA, you should first transmit the byte 0x80 so that these devices can automatically detect the baud rate,
and only then should you send the byte 0xAA so that the Maestro can detect the baud rate. Once all devices have
Pololu Maestro Servo Controller User's Guide © 2001–2014 Pololu Corporation
5. Serial Interface Page 46 of 73