FUSB308B datasheet(8/53 Pages) ONSEMI

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FUSB308B

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• It is not a GoodCRC message

• The calculated CRC is correct

• The SOP* type is enabled

The makeup of the GoodCRC message is formed by the

received SOP* type and the contents of MSGHEADR

When an expected GoodCRC message or a Hard Reset

signaling is received, they will not be replied with a

GoodCRC message (see Note 2 in Figure 6). If a GoodCRC

message received was not expected due to the SOP* type or

mismatched Message ID, the receive state machine will not

send a GoodCRC message and will transition to

PRL_Rx_Report SOP* to inform the TCPM.

If a Hard Reset message is received, the FUSB308B will

reset the RXDETECT preventing the reception of future

messages until the TCPM re−enables it.

Figure 6. Receive State Machine

Message received from PHY (Note 2)

GoodCRC Transmission complete

Start

PRL_Rx_Send_GoodCRC

Actions on entry

Send GoodCRC message to PHY

PRL_Rx_Wait_for_PHY_

message

Actions on entry

PRL_Rx_Report_SOP *

Actions on entry:

Update RECEIVE_STATUS

(ALERT_ L.RXSTAT asserted)

Message discarded

bus Idle(Note 1)

PRL_Rx_Message _Discard

Actions on entry :

If Tx State − Machine active,discard

transmission and assert

ALERT_L.TXDISC

else

Unexpected

GoodCRC received

FUSB308B receives Hard reset |

Cable reset

2. This indication is sent by the PHY when a message has been discarded due to CC being busy, and after CC becomes idle

again (see USB PD Spec).

3. Messages do not include Hard Reset or Cable Reset signals or expected GoodCRC messages (GoodCRC messages are

only expected after the FUSB308B PHY has received the tx message and the FUSB308B Tx state−machine is in the

PRL_Tx_Wait_for_PHY_response state).

Transmit State Machine

To transmit a message, the TCPM must first write the

entire message in the following registers: TXHEADL,

TXHEADH, TXBYTECNT and the TXDATA.

The actual transmission starts when the TCPM writes the

TRANSMIT register.

The TRANSMIT register is where the message selection

is done and it must be written once per transmission.

The TRANSMIT and TXBYTECNT will be reset after

executing a successful or failed transmission.

If the TRANSMIT.RETRY_CNT is set to a number

greater than 0, the FUSB308B will automatically retry

sending the same message if a GoodCRC is not received

within tCRCReceiveTimer. An automatic retry is not

performed when sending Hard−Resets, Cable−Resets, or

BIST Carrier Mode 2 signaling.

The TCPM must not write the TRANSMIT register again

until ALERTL.I_TXSUCC, I_TXFAIL, I_TX_DISC have

been asserted and cleared.

The TCPM will not write the TRANSMIT register to

request a transmission other than a Hard reset until it has

cleared all received message alerts. If a TRANSMIT is

written when ALERTL.I_RXSTAT = 1 or ALERTL.

I_RXHRDRST = 1, the transmit request is discarded and

ALERTL.I_TX_DISC is asserted.

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