User Manual

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 detected the baud rate, Pololu devices that expect a

leading command byte of 0x80 will ignore command packets that start with 0xAA, and the Maestro will

ignore command packets that start with 0x80.

5.h. Serial Example Code

5.h.1. Cross-platform C

The example C code below works on Windows, Linux, and Mac OS X 10.7 or later. It demonstrates

how to set the target of a Maestro channel by sending a Set Target command to its Command Port,

and how to read the position of a channel by sending the Get Position command. The Maestro’s serial

mode needs to be set to “USB Dual Port” for this code to work. You will also need to modify the line

that specifies the name of the COM port device.

5. Serial Interface Page 62 of 102