ANT Forum

Hi,

I am trying to send a message from slave to master periodically at every received sync packet. To do so, The slave waits for the sync packet and after receiving it, it starts transmitting the data immediately (only if the previous transmit was successful or failed). It seems that by doing this, the slave waits for the next sync packet after transmission to send the message making an extra delay of a channel period. In addition, master receives the packet at the next sync packet adding an extra delay resulting in a total delay of two channel periods.

If I try sending acknowledged message, it is never received by the master at the time of transmission and it is received at the next sync packet. However, if I try sending broadcast data, I see that sometimes the message is received at the time of transmission (every other message is received).

The ANT datasheet states that after sending the sync packet, the master goes to receive mode for a short time. How long is that? After receiving the sync packet, how much time do I have to send a message so that it is received by the master quickly? I prefer using acknowledged messages but it seems that it only works sometimes with broadcast data.

Thanks for your help in advance.      

Hi Ali,

If you refer to Figure 9-1 of the ANT Message Protocol and Usage document (Rev 5.0), it explains that this delay is an expected behaviour of bidirectional communication over ANT.

To avoid these delays you may pre-load the transmit buffer of the slave so it is able to transmit data as soon as it receives a message from the master. (This is only possible if the slaves transmission is independent of the data received from the master.)

The ANT Message Protocol and Usage Doc can be found in the documents tab of the downloads page: (http://www.thisisant.com/resources/ant-message-protocol-and-usage/)