User Manual

Data Sheet / User Manual RB-TW-2400
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5 Operation
5.1 Overview
The API module’s job is it to serve the interface to external devices (in most cases this is the
Application Controller (AC). It provides a set of commands available for the external device
(hereinafter referred to as AC).
5.2 Communication Interface
The RC provides two communication interfaces which can be selected by the user. These two interfaces are
mutually exclusive and must be selected by the user before boot up. The protocol is the same on both
interfaces with minor differences explained later on. The user’s device (which controls the RC) is
hereinafter referred to as application controller (AC).
Hardware Interface
Two interfaces provided by the RC are the serial peripheral interface (SPI) and a universal
asynchronous receiver transmitter (UART). On the SPI-interface the RC has the slave role, thus the
clock is provided by the user. Since the RC needs time for command processing and is also able to
initiate a communication cycle on its own, two additional handshake lines (Ready & Indication) are
used. The usage is explained in the next sub section. The SPI-interface is selected by default if the
‘API-Select’-pin is not connected to Vcc. If the ‘API-Select’-pin is connected to Vcc during boot up
the UART-interface is selected. The UART-interface operates at 19200 Baud with 8 databits, 1 stopbit
and no parity. It only utilizes the two data-lines (TXD, RXD) and ground, handshake-lines are not
foreseen. Protocol on the UART-interface is similar to the protocol used on the SPI-interface it is also
described in this section.