Robotis Dynamixel DX-117 - Manual (Page 29)

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DYNAMIXEL DX-Series
Appendix
RS-485 RS-485 is a protocol used for serial communication which operates by forming a bus
with multiple clients connected to a single line. Thus, transmission and reception cannot
occur at the same time, and while one client is transmitting, all the other clients need to
be in input mode. The Main Controller that controllers the Dynamixel actuators sets the
RS485 communication direction to be input mode, and only when it is transmitting an
Instruction Packet, it changes the direction to be output mode.
Return Delay Time The time it takes for the Dynamixel actuator to return the Status Packet after receiving
an Instruction Packet. The Default Value is 160 uSec and can be changed via the
Control Table at Address 5. The Main Controller needs to change the RS485
communication direction during the Return Delay Tim after sending an instruction packet.
485 Direction
For RS-485, the timing to change the direction to receiving mode right after the ending
of the transmission is important. The bit definitions within the register that indicates
UART_STATUS are as the following.
TXD_BUFFER_READY_BIT: Indicates that the transmission DATA can be loaded into
the Buffer. Note that this only means that the SERIAL TX BUFFER is empty, and does
not necessarily mean that the all the data transmitted before has left the CPU.
TXD_SHIFT_REGISTER_EMPTY_BIT: Set when all the Transmission Data has
completed its transmission and left the CPU.
The TXD_BUFFER_READY_BIT is used when one byte is to be transmitted via the
serial communication channel, and an example is shown below.
TxDByte(byte bData)
{
while(!TXD_BUFFER_READY_BIT); //wait until data can be loaded.
SerialTxDBuffer = bData; //data load to TxD buffer
}
Instruction Packet Status Packet
Return Delay Time
RS485 Direction Output Duration