Echelon FTXL Hardware - Manual (Page 76)

68 Using the Bring-Up Application to Verify FTXL Hardware Design
To write each byte, the application must first wait until LonTransceiverIsBusy()
returns FALSE, and then call LonWriteTransceiverDataRegister(). After the
write is complete, the FTXL Transceiver has the token, and either sends a data
packet or passes the token back. The application must read the data packet or
token by reading first the length byte (which indicates the number of data bytes)
and then reading all data bytes. If the length byte is 0x0, there is no data. To
read each byte, the application must first wait until LonTransceiverIsBusy()
returns FALSE, and then call LonReadTransceiverDataRegister().
The FTXL Transceiver enters a “fast I/O” mode during certain portions of a data
transfer. During these times, the host processor must read or write the next byte
within a certain amount of time, or the FTXL Transceiver assumes that it has
lost synchronization with the host and resets. The timeout period is a function of
the FTXL Transceiver clock speed. Table 22 lists the timeout values. Note that
the application must respond within the minimum time shown in the table to
ensure that the FTXL Transceiver does not timeout.
Table 22. Fast-I/O Mode Timeout Values
Transceiver Clock Rate Timeout
5 MHz 1.68 to 3.36 seconds
10 MHz 0.84 to 1.68 seconds
20 MHz 0.42 to 0.84 seconds
40 MHz 0.21 to 0.42 seconds
The FTXL Transceiver enters fast-I/O mode under the following conditions:
• After the application reads the first byte of a packet (the length byte), the
FTXL Transceiver enters fast-I/O mode until all bytes in the packet have
been read.
• After writing a zero length byte (to pass the NULL token), the FTXL
Transceiver enters fast-I/O mode until the token byte has been written.
• After writing the first data byte of a packet, the FTXL Transceiver enters
fast-I/O mode until all subsequent data bytes in the packet and the token
byte have been written. Note that the FTXL Transceiver does not go into
fast-I/O mode upon receiving the length byte – only after the first data byte
(second byte of the frame) has been written.
Interrupt
The interface includes an interrupt signal. The FTXL Transceiver interrupts the
Nios II processor under the following conditions:
• When the FTXL Transceiver has data to be sent to the host, whether it
has the token or not.
• If the FTXL Transceiver has the token, and is ready to pass the NULL
token.
• After the FTXL Transceiver has received a non-zero length byte from the
host.