 2004 - 2015 Microchip Technology Inc.

DS00001898A-page 17

USB3280

7.0

FUNCTIONAL OVERVIEW

FIGURE 2-1: on page 5 shows the functional block diagram of the USB3280. Each of the functions is described in detail

below.

7.1

Modes of Operation

The USB3280 supports an 8-bit bi-directional parallel interface.

• CLKOUT runs at 60MHz

• The 8-bit data bus (DATA[7:0]) is used for transmit when TXVALID = 1

• The 8-bit data bus (DATA[7:0]) is used for receive when TXVALID = 0

7.2

System Clocking

This block connects to either an external 24MHz crystal or an external clock source and generates a 480MHz multi-

phase clock. The clock is used in the CRC block to over-sample the incoming received data, resynchronize the transmit

data, and is divided down to 60MHz (CLKOUT) which acts as the system byte clock. The PLL block also outputs a clock

valid signal to the other parts of the transceiver when the clock signal is stable. All UTMI signals are synchronized to the

CLKOUT output. The behavior of the CLKOUT is as follows:

• Produce the first CLKOUT transition no later than 5.6ms after negation of SUSPENDN. The CLKOUT signal fre-

quency error is less than 10% at this time.

• The CLKOUT signal will fully meet the required accuracy of ±500ppm no later than 1.4ms after the first transition

of CLKOUT.

In HS mode there is one CLKOUT cycle per byte time. The frequency of CLKOUT does not change when the PHY is

switched between HS to FS modes. In FS mode there are 5 CLKOUT cycles per FS bit time, typically 40 CLKOUT cycles

per FS byte time. If a received byte contains a stuffed bit then the byte boundary can be stretched to 45 CLKOUT cycles,

and two stuffed bits would result in a 50 CLKOUT cycles.

Figure 7-1 shows the relationship between CLKOUT and the transmit data transfer signals in FS mode. TXREADY is

only asserted for one CLKOUT per byte time to signal the SIE that the data on the DATA lines has been read by the

PHY. The SIE may hold the data on the DATA lines for the duration of the byte time. Transitions of TXVALID must meet

the defined setup and hold times relative to CLKOUT.

FIGURE 7-1:

FS CLK RELATIONSHIP TO TRANSMIT DATA AND CONTROL SIGNALS