The following explains the use of the Input MTU and Output MTU buffers.
The frame length and the operational configuration result in different combinations of control bytes and data bytes on the serial interface.
Each frame contains at least one control byte. Depending on the frame length, the frame may be split into several segments and MTUs.
When receiving data, the position of the data and control bytes within the MTU is determined by the configuration: see Multiple Segments / Segment Size and Block Forward.
When transmitting data, the procedure and structure can be selected as required by the application.
Depending on the combinations, the following options are available:
oMaximizing control and monitoring of the individual steps
oMaximizing data throughput
Maximizing Control and Monitoring of the Individual Steps
oNo MTU block forwarding
oSingle segment within the MTU
oSegment size does not exceed MTU size
Advantages:
oClearly structured control bytes are at the start of the MTU.
Disadvantages:
oLow data throughput
oForwarding of MTU blocks
oMultiple segments within the MTU
oSegment size exceeds MTU size
This configuration optimizes data throughput.
Advantages:
oHigh data throughput by using forwarding and multiple segments in an MTU
Disadvantages:
oGreater programming effort
In the event of a cycle error detected (sequence number lost) or an occupied transmission buffer, error handling is identical: the procedure must be repeated starting at the first unacknowledged sequence number.
Receipt of a valid sending sequence number only acknowledges data transfer into the transmission buffer: it is not acknowledgment that the frame has actually been sent. Depending on the transfer distance, acknowledgment of the sending sequence number can take several cycles.
A change in value of the receive sequence number acknowledgment in the InputSequence indicates that new data received from the module are pending. Each receive sequence number must be acknowledged using the receive sequence number acknowledgment in the OutputSequence; otherwise, the connection to the module is disconnected.
