CY7C68003

Document Number: 001-15775 Rev. *I

Page 11 of 27

USB Data Transmit (PID)

In this mode, the link transmits data on the USB with a Packet Identifier (PID). The link first drives a TX CMD byte as illustrated in

Figure 9 on page 11 to transmit a USB packet. The link sets the Command Code to 01b (Transmit) and places the USB Packet Identifier

(PID) on DATA[3:0] (see Table 9 on page 9). TX2UL throttles the data using NXT such that the link provides the next byte in the cycle

after NXT is detected as high.

Figure 8. USB Data Transmit (PID)

USB Packet Receive

As shown in Figure 10 on page 12, when TX2UL receives the USB data it gains ownership of the data bus by asserting DIR. The DIR

is previously either high or low. If DIR is low (see Figure 9), TX2UL asserts both DIR and NXT so that the link knows immediately that

this is a USB receive packet. If DIR is high (see Figure 10 on page 12), TX2UL deasserts NXT and drives an RX CMD with the RxEvent

field set to the RxActive state. The TX2UL starts driving data in the following cycle or outputs RX CMD until USB data is available.

Valid USB packet data is presented to the link by asserting NXT and placing a byte on the bus. When NXT is low, TX2UL drives the

RX CMD byte. All RX CMD changes during the USB packet receive are signaled when NXT is low. If NXT is never low during the

packet receive, all RX CMD changes are replaced with a single RX CMD update. This update is sent at the end of the USB packet

receive, when the ULPI bus is available. The RX CMD update always conveys the current RX CMD values and not the previous one.

Figure 9. USB Receive While DIR is Previously Low

CLOCK

DATA[7:0]

DIR

STP

NXT

D1

TX CMD (PID)

D2

D3

CLOCK

DATA[7:0]

DIR

STP

NXT

Turn around

RX CMD

PID

D1

RX CMD

D2

D3

Turn around

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