Motorola USB08 - page 71

Universal Serial Bus (USB) Interface

Device Management with Endpoint 0

USB08 Evaluation Board Designer Reference Manual

MOTOROLA Universal Serial Bus (USB) Interface 71

The type of standard request is coded in the field bRequest. For

continuation of the enumeration, the host should send the standard

device request SET_ADDRESS and the handleSETUP() routine should

branch to the function setAddress().

The function first validates the contents of the fields of SetupBuffer. In

the case of an error, a STALL handshake is initiated to give the host

problem feedback.

Before the device address in the field wValue is finally accepted, the

MCU has to prepare the transmission of a receive acknowledgment.

This acknowledgement still is completed using the old device address

zero. An additional safety feature is the mandatory control transfer stat us

stage.

The handshake takes place via a telegram with a data length of zero,

which is requested by the host by means of an IN transaction. For this

purpose, the length TP0SIZx is defined as zero and the TX0E bit is set

in the USB control register 0 (UCR0). This enables the transmitter of the

endpoint 0.

This handshake transaction always uses a DATA1 packet; therefore,

T0SEQ is set.

The routine setAddress() now returns to handleSETUP() where the

receive interrupt for EP0 is re-enabled. Finally, the MCU terminates the

interrupt service routine isrUSB().

The device address is still located in the SetupBuffer. The service

routine isrUSB() is again activated by a transmit interrupt for EP0. After

decoding, if it was determined that the cause of the interrupt was an IN

Bit 7654321Bit 0

Read:

T0SEQ

Tx0E Rx0E TP0SIZ3 TP0SIZ2 TP0SIZ1 TP0SIZ0

Write:

Reset:00000000

= Unimplemented

Figure 4-7. USB Control Register 0 (UCR0)