Manual

Mode 4: Packetized Serial Mode
Packetized Serial uses TTL level multi-byte serial commands to set the motor speed and
direction. Packetized 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 SyRen 10 or 20. Because of this,
multiple SyRens 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. Packetized serial uses an address byte to select the target device. The
baud rate is selected automatically by sending the bauding character (170 in decimal, AA in hex)
before any commands are sent.
Packet Overview
The packet format for the SyRen 10 and 20 consists of an address byte, a command byte, a data
byte and a seven bit checksum. Address bytes have value greater than 128, and all subsequent
bytes have values 127 or lower. This allows multiple types of devices to share the same serial
line.
An example packet and pseudo-code to generate it are shown in Figures 7.1 and 7.2
Packet
Address: 130
Command : 0
Data: 64
Checksum: 66
Void DriveForward(char address, char speed)
{
Putc(address);
Putc(0);
Putc(speed);
Putc((address + 0 + speed) & 0b01111111);
}
Figure 7.1: Example 50% forward Figure 7.2: Pseudocode to generate 7.1
Baud Rate Selection:
Packetized Serial operates with an 8N1 protocol – 8 data bytes, no parity bits and one stop bit.
The baud rate is automatically calculated by the first character sent. This character must be 170
(binary 10101010) and must be sent before any serial communications are done. It is not possible
to change the baud rate once the bauding character has been sent. The valid baud rates are 2400,
9600, 19200 and 38400 baud. Until the bauding character is sent, the driver will accept no
commands and the green status light will stay lit. Please note that the Syren 10 and SyRen 25
may take up to a second to start up after power is applied, depending on the power source being
used. Sending the bauding character during this time period may cause undesirable results.
When using Packetized Serial mode, please allow a two second delay between applying
power and sending the bauding character to the drivers.