DS80PCI402: How to reset Rx Detect State Machine by SMBus

Hi Nick,

We have verified that the steps mentioned in Tablenote (1) of Table 4 resets the Rx Detect State Machine. Only two register writes are needed.

It may be possible that we need to clarify with the customer what the Rx Detect State Machine does.

Assuming RXDET Pin = Float, whenever the DS80PCI402 powers on or the PRSNT# pin is toggled, the DS80PCI402 enters automatic Rx-Detect. This means that the DS80PCI402 Tx will send a pulse to determine whether there is an endpoint with an appropriate load. Note that RXDET is not the same as the DS80PCI402 input signal detect. RXDET tests for an endpoint to receive the output of the DS80PCI402.

RX Detect Sequence is as follows (see Table 4):

1. When RXDET = Float and no endpoint is present, the output of the DS80PCI402 is Hi-Z. This can be verified by measuring the resistance between Tx output and VDD supply.

2. When an endpoint is detected, the DS80PCI402 will automatically enable an input termination of 50-Ohms to VDD. This can be verified by measuring 50-ohms between Tx output and VDD supply.

3. In automatic behavior, once the RX Detect State machine detects a connection, the state machine will not reset unless a power-on reset or PRSNT# pin toggle occurs. Therefore, once a 50-ohm input termination is connected, it will remain this way even if there is an endpoint disconnection without power-on reset.

By resetting the DS80PCI402 Rx Detect State Machine, the DS80PCI402 will restart its search for a valid endpoint.

How is your customer testing to verify this behavior?

Michael