Innovate Motorsports OT-2 SDK - Manual (Page 37)

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Unlike In Band mode, MTS packets are not ‘pushed’ to the virtual OUT connection in
Expert Modes. You can poll the last MTS packet passed with the ‘b’ command which is
available in all expert modes.
All three modes offer very similar commands, but the parameters are tweaked to match
the physical requirements of the underlying protocol. In general, all modes offer a way to:
• Set Data Rate
• Send, and optionally receive a specified amount
• Just Receive
• Set filters on received data
• Control the Vehicle LED on the OT-1b/2
• Exit back to Setup Mode
There are some specialized commands for several of the protocols, but this is the basics.
At first glance you might wonder why there is both a Send/Receive and a Receive only.
One reason is timing. Depending on the host operating system (uncontrolled yields) or
transport (bit errors on a network), the Host may not be able to meet the timing
requirements for transactions for a given protocol. On the other hand, some applications
require passive monitoring of other activity on the bus.
It also should be clear from this basic command structure that the interface is
fundamentally half duplex. That is, you are either sending, or specifically listening to the
OBD-II interface in question. And, when you are listening, you are listening for either a
period of time or an expected number of responses.
There are some limitations to this sort of interface model. However, the primarily reason
that it was selected was for best performance under as many network conditions as
possible. A full duplex model would involve data tricking in both directions at variable
rates. This sort of communication model is most likely to run into timing and throughput
problems in a TCP connection. Half duplex, in the form of command/response, helps
eliminate problems such as ‘delayed ACK’ (see the section on special considerations for
Wi-Fi later in this document for more details).