User Manual

Protocol support: Radio Access Protocol (RAP)
Integrator’s Guide – RIM 801D OEM Radio Modem
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When to choose RAP over NCL
RAP helps application developers simplify software development on small-
memory devices like PDAs, vending machines, POS terminals, alarm
panels, and other embedded systems. With NCL, the amount of software
required to implement the NCL interface can be greater than the available
memory. With RAP, a complete DataTAC radio interface needs only 1 to 3
Kbytes, compared to the typical NCL implementation that requires generally
more Kbytes. This increases the memory available for applications.
The RIM 801D OEM radio modem includes on-board support for both NCL
and RAP. Even when in RAP mode, the RIM 801D can detect certain NCL
frames arriving on the serial port. This will cause the radio to automatically
switch to NCL mode. RIM has included both protocols on the RIM 801D to
maintain backward compatibility with existing applications.
RAP implementation assumptions
As a communication protocol, RAP was created under the following
assumptions:
• Simple serial packet interface is easiest to test and verify.
• Microcontrollers with limited memory are able to send a packet,
receive a packet, control the radio, and obtain status from the radio.
• Microcontrollers must add code to support a RAP radio.
• RAP is simple enough that an API is not required.
• Data integrity is assured with checksums, but the checksums are
optional if there are no CPU cycles to spare for the calculation.
• The serial link used by RAP is not prone to bit errors. However,
embedded applications might miss individual characters due to
receiver over-runs while they are busy handling other functions.
RAP provides recovery capability for missed characters.
• Data is formatted by the microcontroller and sent through RAP;
RAP does not have any SDU formatting functions.