Echelon FTXL Hardware - Manual (Page 81)

FTXL Hardware Guide 73
Read Handshake
Handshake (D0) busy
A0 high -> D0 is handshake
CS~ low -> transfer in progress
RW~ high -> read
Figure 29. Reading Status Register during Reset
Token Passing Test
After the reset test runs successfully, the Token Passing Test repeatedly passes
the null token between the Nios II processor and the FTXL Transceiver under
program control (that is, without interrupts). This test verifies the status
register to ensure that it reports busy immediately after write operations, and
verifies that the reset capture register does not report reset during normal
operation. Reading and writing to the data register is partially verified.
However, in this test, both the application and the FTXL Transceiver write zero
bytes to the data register.
This test and the remaining tests use a utility function (waitUntilReady()) to
wait for the FTXL Transceiver to become ready. This function checks the reset
capture register to detect resets, and includes a basic timeout mechanism.
Figure 30 on page 74 shows the state of the signals while writing the length byte.