User Guide

Mode 3: Simplified Serial Mode
Simplified serial uses TTL level single-byte serial commands to set the motor speed and
direction. This makes it easy to interface to microcontrollers and PCs, without having to
implement a packet-based communications protocol. Simplified serial is a one-direction only
interface. The transmit line from the host is connected to S1. The host’s receive line is not
connected to the Sabertooth. Because of this, multiple drivers can be connected to the same serial
transmitter. If using a true RS-232 device like a PC’s serial port, it is necessary to use a level
converter to shift the –10V to 10V rs-232 levels to the 0v-5v TTL levels the Sabertooth is
expecting. This is usually done with a Max232 type chip. If using a TTL serial device like a
microcontroller or a USB-to-TTL serial converter, the TX line of the microcontroller may be
connected directly to S1.
Because Sabertooth controls two motors with one 8 byte character, when operating in Simplified
Serial mode, each motor has 7 bits of resolution. Sending a character between 1 and 127 will
control motor 1. 1 is full reverse, 64 is stop and 127 is full forward. Sending a character between
128 and 255 will control motor 2. 128 is full reverse, 192 is stop and 255 is full forward.
Character 0 (hex 0x00) is a special case. Sending this character will shut down both motors.
Baud Rate Selection
Simplified Serial operates with an 8N1 protocol – 8 data bytes, no parity bits and one stop bit.
The baud rate is selected by switches 4 and 5 from the following 4 options:
2400 Baud: 01x00x 9600 Baud: 01x10x
19200 Baud: 01x01x 38400 Baud: 01x11x
What baud rate to use is dependent on what your host can provide and the update speed
necessary. 9600 baud or 19200 baud is recommended as the best starting points. If
communication is unreliable, decrease the baud rate. If communications are reliable, you may
increase the baud rate. The maximum update speed on the Sabertooth is approximately 2000
commands per second. Sending characters faster than this will not cause problems, but it will not
increase the responsiveness of the controller either.
The baud rate may be changed with power on by changing the DIP switch settings. There is no
need to reset or cycle power after a baud rate change.
There are 2 operating options for Simplified Serial, selected by the position of Switch 6.