MC908JB16DWE Datasheet, PDF (172/332 Pages) Freescale Semiconductor, Inc – Microcontrollers

Universal Serial Bus Module (USB)
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
register to determine if a given transaction is targeting the MCU USB
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.
Technical Data
172
Universal Serial Bus Module (USB)
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor