7643 datasheet(284/424 Pages) RENESAS

284 / 424 page

Rev.2.00

Aug 28, 2006

page 163 of 202

7643 Group

REJ09B0133-0200

APPLICATION

2.6 USB

2.6.10 Notes on USB function

(1)

USB receive

q For endpoints 1 or 2, when there are two packets of data in the OUT FIFO, after reading out

the max OUT packet size of data, one packet of data will remain in the OUT FIFO. In this case,

even if the OUT_PKT_RDY flag is set to “0”, it will return to “1” after 83ns (Vcc = 5V, f(XIN) =

24MHz).

q Read one packet data from the OUT FIFO before clearing the OUT_PKT_RDY flag. If the

OUT_PKT_RDY flag is cleared while one packet data is being read, the internal Read pointer

cannot operate normally.

(2)

USB transmit

q Determine the number of data packets in the IN FIFO by the value of the IN_PKT_RDY bit and

the TX_NOT_EPT flag. For more details, refer to Table 2.6.2 in [Section 2.6.4 USB transmit].

q For endpoints 1 or 2, to transmit a NULL packet, set the IN_PKT_RDY bit to “1” without writing

data to the FIFO.

(3)

External circuits

q Figure 2.6.58 shows a peripheral circuit example of the external capacitor (Ext. Cap) pin.

Connect a low-frequency 2.2

µ F Tantal capacitor and a 0.1 µF ceramic capacitor (X7R type

recommended) in parallel between the Ext. Cap pin and the Vss pin.

In addition, connect a 1.5k

Ω (±5%) resistor between the Ext. Cap pin and the D+ pin.

q The Full-Speed USB2.0 specification requires a driver-impedance of 28 to 44

Ω (refer to Clause

7.1.1.1 Full-Speed (12Mb/s) Driver Characteristics).

In order to meet USB specification impedance requirements, connect a resistor (27 to 33

Ω

recommended) in series to the USB D+ and D- pins.

In addition, in order to reduce the ringing and control the falling/rising timing of USB D+/D- and

a crossover point, connect a capacitor (69pF recommended) between the USB D+/D- pins and

the Vss pin if necessary.

The values and structure of those peripheral elements depend on the impedance characteristics

and the layout of the printed circuit board. Accordingly, evaluate your system and observe

waveforms before actual use and decide use of elements and the values of resistors and

capacitors.

q Make sure the wiring of the USB connector or USB cable is as short as possible.

q Make sure the USB D+/D- lines do not cross any other wires.

Keep a large GND area to protect the USB lines.

Also, make sure you use a USB specification compliant connecter for the connection.

q All passive components must be located as close as possible to the LPF pin.

For recommended values, see Figure 2.6.59.

q An insulation connector (Ferrite Beads) must be connected between AVss and Vss pins and

between AVcc and Vcc pins.

q Connect 0.1

µF and 4.7 µF capacitors in parellel between the Vss and Vcc pins and between

the AVss and AVcc pins.

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