Connecting Channel Bonding Ports

The channel bonding operation requires connecting the master GTY transceiver RXCHBONDO port to the RXCHBONDI port of all slaves in the group. Only GTY transceivers belonging to the same column can be channel bonded together. A direct connection is required for adjacent GTY transceivers. To directly connect a master to a slave:

1. Connect the RXCHBONDO port of the master to the RXCHBONDI port of the slave.
2. Tie the RXCHBONDMASTER of the master transceiver High.
3. Tie the RXCHBONDSLAVE of each slave transceiver High.

When GTY transceivers are directly connected, meeting the timing constraints becomes difficult as the transceivers get further apart. The solution to this problem is to connect the transceivers in a daisy chain. Daisy chaining is performed using the RXCHBONDLEVEL[2:0] ports to allow additional pipeline stages between the master and the slave. The RXCHBONDO port of each slave is used as a pipeline stage in the RXCHBONDO path from the master. The following figures show two daisy-chain examples.

To set up a daisy chain, the GTY transceivers are first connected using RXCHBONDO and RXCHBONDI to create a path from the RXCHBONDI port of each slave to the RXCHBONDO port of the master. The following steps describe how to set the RXCHANBONDLEVEL for the GTY transceivers in the chain:

1. Set the RXCHANBONDLEVEL of the master to 7.
2. Set the RXCHANBONDLEVEL of each slave to the RXCHANBONDLEVEL of the GTY transceiver driving the slave’s RXCHBONDI port minus 1.
3. Find the slave with the lowest level. Subtract this level from the RXCHANBONDLEVEL of all GTY transceivers so that the lowest slave has level 0 and the master has the minimum level required to service all the slaves. When using a 4-byte internal datapath (RX_INT_DATAWIDTH = 1), do not have the master exceed RXCHANBONDLEVEL = 3.

When the connections between channel bonding ports among GTY transceivers are being decided, the designer must remember that RXCHBONDI and RXCHBONDO belong to the RXUSRCLK clock domain. Meeting the timing constraint of RXUSRCLK becomes increasingly difficult as RXUSRCLK increases in frequency and as directly connected transceivers get further apart. As long as timing constraints are met, channel bonding transceivers together in adjacent SLRs is possible.

Selecting a GTY transceiver in the middle of the GTY transceiver column to be the master for channel bonding allows for the most flexibility when connecting channel bonding ports. When the channel bonding master is in the middle of the GTY transceiver column, connections can be made to GTY transceivers north and south of the master. Because of the GTY transceiver dedicated clock routing structure, an additional benefit of having the channel bonding master at the center of the GTY transceiver column is that up to 20 GTY transceivers can be channel bonded together using a single clock pin pair.

As long as timing constraints are met, there is no limit to the number of GTY transceivers that can be on a particular RXCHANBONDLEVEL.