Hi guys

I have a question regarding acknowledgement (ACK) between two devices. So my question is: How to tell the ACK is received?

Say I have a Master and a Slave, they need to communicate. That's what would I am planing to do:
Master: send a stream of message with CRC.
Slave: received message and replay with ACK.

So how can the slave tells the master has received the ACK? I can't get the master to reply with another ACK, because if I do, they will go on forever. So how do we handle a situation like this?

Thanks guys!!

 

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From the sender's point of view, for each transmission it requires a response (ACK). Sometimes, it takes a few times to "synchronize the communications"... If the sender receives an "I don't understand" (NAK), it retries its last operation.

Are you there?
I don't understand
Are you there?
I don't understand
Are you there?
I don't understand
Are you there?
I'm here and got your question!
Here's my message for you.
I'm here and got your message!
I'm done...
I understand

There are several protocols for communications. That was taken from a description of serial communications and generalized from TCP/IP handshaking. XON/XOFF protocol is similar as well.

 

In general:

1. The receipt of a NAK causes re-transmission.
2. The lack of an ACK causes re-transmission after a timeout interval.
3. The receipt of an ACK allows the transmission of the next packet.

 

In general:

1. The receipt of a NAK causes re-transmission.
2. The lack of an ACK causes re-transmission after a timeout interval.
3. The receipt of an ACK allows the transmission of the next packet.

Missed point 2! Thanks for adding it, Papabravo.