4. CAN Message Exchange Architecture

4.1 Architecture

(a) Position Control is executed at approximately 1ms (or 960us) intervals.

(b) Reserved

(c) Upon receiving an OP CMD Msg, OP RESP Msg0/1 return the CAN bus with data from the previous control loop (Rolling count is preserved). Due to internal CAN initialization, the very first OP CMD Msg(NORMAL_REQ) may be ignored once. (This limitation does not apply to PBIT_REQ.)

(d) After powered up, if there is no incoming OP CMD Msgs, the servo output shaft is controlled at the current position.

4.2 OP CMD Msg Handling

(a) OP CMD Msg transmitted from the host system is processed as follows. (e.g., host system OP CMD Msg Tx Rate = 20ms).

Figure 8. CAN Msg Handling

(b) For a single channel:

· If 1 OP CMD Msg is received during the control period, it is processed.

· If 2 OP CMD Msgs are received, the first one is processed.

· If 0 messages are received, the previous period’s message is reused.

When two channels are used, the first arriving OP CMD Msg is processed. Therefore, if OP CMD Msgs with different command values are alternately received from each channel, a race condition may occur. To prevent this, the host system must send identical or nearly identical OP CMD Msgs on both channels at predefined timing intervals.

(c) Upon receipt, the OP CMD Msg is processed immediately by the internal ISR(Interrupt Service Routine), and the corresponding OP RESP Msgs are sent with minimal delay.