Cypress EZ-USB Series 2100 User's Guide download pdf (Page 201)

EZ-USB FX2™/AT2™/SX2™

Reset and Power Considerations

The easiest solution is to set the DISCON bit to 0, so your

device will pull up D+ immediately. See chapter 3.5 in the FX2

technical reference manual for more information on the

DISCON and 400-kHz bits.

2. Respond to Reset within 100 ms

Typical FX2 designs easily meet this requirement, since the

first USB reset is handled automatically by the FX2 hardware.

3. Set-up Packet within 500 ms

This specification requires that all SETUP packets get replies

in a timely fashion. If the RENUM bit is set, this means that

there cannot be any tasks that delay the TD_Poll() loop. If this

is not practical in your design, SETUP packets can be

processed in an ISR. The CY4611 reference design provides

an example of SETUP processing in an ISR. As the code

fragment in Figure 3 shows, setting up the SUDAV interrupt

takes very little effort:

4. No D+ without VBUS

Specification section 7.1.5 states, “The voltage source on the

pull-up resistor must be derived from or controlled by the

power supplied on the USB cable such that when VBUS is

removed, the pull-up resistor does not supply current on the

data line to which it is attached.” This is not an issue for

bus-powered devices. For self-powered devices, this

requirement means that an I/O pin must be used to sense

VBUS. Don’t forget to pull the pin down, or it will not always

go to 0 when you’re disconnected!

On FX2, firmware must poll this pin regularly and disable the

pull-up resistor when VBUS is removed. Using the wake-up

line for this purpose allows the design to go to sleep until

VBUS is reapplied.

The AT2 provides a dedicated VBUS sense pin.

On SX2, the host CPU is responsible for disconnecting the

pull-up via the DISCON bit in the IFCONFIG register.

EZ-USB FX2, EZ-USB SX2, and EZ-USB AT2 are trademarks of Cypress Semiconductor

Corporation. All product and company names mentioned in this document are the trademarks

of their respective owners.

Approved AN065 10/14/03 kkv

EZUSB_IRQ_ENABLE(); // Enable USB interrupt (INT2)

EZUSB_ENABLE_RSMIRQ(); // Wake-up interrupt

INTSETUP |= (bmAV2EN); // Enable INT 2 auto vectoring

USBIE |= bmSUDAV | bmSUSP | bmURES | bmHSGRANT; // Enable selected interrupts

EA = 1; // Enable 8051 interrupts

// Setup Data Available Interrupt Handler

void ISR_Sudav(void) interrupt 0

{

EZUSB_IRQ_CLEAR();

INT2CLR = bmSUDAV; // Clear SUDAV IRQ

SetupCommand();

}

Figure 3.

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