User`s guide

9. Using the TTL Serial Port

The Orangutan SVP’s USB Connection provides a serial port called the Pololu Orangutan SVP TTL Serial

Port which allows two-way communication between a personal computer and TTL-level serial devices at baud

rates between 300 bps and 115200 bps. This serial port can be used for communication between a computer and

an external serial device besides the AVR. It can also be used to debug the serial communication between the

AVR and an external serial device. If you want to communicate directly between the AVR and a computer, we

recommend using the USB Communications Port (see Section 8).

The bytes sent from the computer on this serial port will be transmitted on the TX line. Bytes received on the

D/RX line will be sent back to the computer. The bytes are sent and received eight bits at a time, non-inverted,

with no parity and one stop bit (8N1).

To use the TTL Serial Port, you must first determine what port name the operating system has assigned it.

To determine the port name in Microsoft Windows, open the Device Manager, expand the “Ports (COM & LPT)”

list, and look for the Pololu Orangutan SVP TTL Serial Port entry. The port name will be at the end of this line

in parentheses (e.g. “COM4”). In Windows, a given device will always be associated with the same port unless

you manually change its port assignment in the Device Manager (see Section 5.a).

Windows Vista device manager showing the Pololu Orangutan SVP.

To determine the port name in Linux, type ls /dev/ttyACM*. The port name will be one of the devices listed

there. If there are only three ports, then the TTL Serial Port will be /dev/ttyACM2 (the programmer will be /dev/

ttyACM0 and the USB communications port will be /dev/ttyACM1). If you see more than three ports, then you

should look at the output from dmesg when you plug in the Orangutan SVP to see which three ports are created;

the third port is the TTL Serial Port. In Linux, the port name depends on how many other devices are using the

USB CDC ACM driver to create virtual serial ports at the time the Orangutan SVP is plugged in.

After determining the port name, you can use any serial port software to communicate on that port.

There are many free terminal programs available, including PuTTY [http://www.chiark.greenend.org.uk/~sgtatham/

putty/] (Windows or Linux), Tera Term [http://hp.vector.co.jp/authors/VA002416/teraterm.html] (Windows), and Br@y

Terminal [http://sites.google.com/site/terminalbpp/] (Windows). To use any of these terminal programs, you must

specify the port name determined above, and the baud rate.

9. Using the TTL Serial Port Page 34 of 41