Echelon FT 3150 Smart Transceiver - Manual (Page 61)

FT 3120 / FT 3150 Smart Transceiver Data Book 55
Parallel I/O Objects
Once in possession of the write token, the device (FT Smart Transceiver or a host processor) can transfer up to 255
bytes of data. The stream of data bytes is preceded by the command and length bytes. The token holder keeps
possession of the token until all data bytes have been written, after which the token is passed to the attached device.
The same process may now be repeated by the other side or, alternatively, the token can be passed back without any
data. The timing relationship between the various FT Smart Transceiver signals involved in this process is shown in
the following timing diagrams.
Resynchronization Procedure: The following procedure applies to master/slave A and master/slave B
configuration. The master initiates the resynchronization with a RESYNC (0x5A) command, and the slave
acknowledges with an ACKSYNC (0x07). If the slave does not respond, the master continues to send the RESYNC
until the slave responds correctly.
MASTER SLAVE
(Owns Token)
Write RESYNC
// master initiates resynchronization (0x5A)
Read RESYNC
Write EOM // end of message (EOM=0x00)
Process EOM
Write ACKSYNC
// slave acknowledges resynching (0x07)
Read ACKSYNC
Write EOM
Process EOM // master owns token when reset
(Owns Token)
Master writes buffer to slave: Enter RD/_WR=0.
MASTER
SLAVE
(Owns Token)
Write XFER
// master has data to write (XFER=0x01)
Read XFER
Write (length) // length=number of bytes of data
MASTER
HAS
TOKEN
MASTER
SLAVE
HAS
TOKEN
SLAVE
FT SMART
TRANSCEIVERS
WRITE
DATA
PASS
TOKEN
CMP_
RESYNC
WRITE
DATA
PASS
TOKEN
CMP_ACK
RESYNC
Figure 3.21 Handshake Protocol Sequence Between the Master and the Slave