M68HC08 datasheet(172/332 Pages) FREESCALE

172 / 332 page

Universal Serial Bus Module (USB)

Technical Data

MC68HC908JB16 — Rev. 1.1

172

Universal Serial Bus Module (USB)

Freescale Semiconductor

11.5.1.3 Address Field (ADDR)

The address field is a 7-bit number that is used to select a particular USB

device. This field is compared to the lower seven bits of the UADDR

device.

11.5.1.4 Endpoint Field (ENDP)

The endpoint field is a 4-bit number that is used to select a particular

endpoint within a USB device. For the MCU, this will be a binary number

between 0 and 2 inclusive. Any other value will cause the transaction to

be ignored.

11.5.1.5 Cyclic Redundancy Check (CRC)

Cyclic redundancy checks are used to verify the address and data

stream of a USB transaction. This field is five bits wide for token packets

and 16 bits wide for data packets. CRCs are generated in the transmitter

and sent on the USB data lines after both the endpoint field and the data

field.

11.5.1.6 End-of-Packet (EOP)

The single-ended 0 (SE0) state is used to signal an end-of-packet

(EOP). The single-ended 0 state is indicated by both D+ and D– being

below 0.8V. EOP will be signaled by driving D+ and D– to the single-

ended 0 state for two bit times followed by driving the lines to the idle

state for one bit time. The transition from the single-ended 0 to the idle

state defines the end of the packet. The idle state is asserted for one bit

time and then both the D+ and D– output drivers are placed in their high-

impedance state. The bus termination resistors hold the bus in the idle

state. Figure 11-7 shows the data signaling and voltage levels for an

end-of-packet transaction.

M68HC08 Datasheet(PDF) 172 Page - Freescale Semiconductor, Inc