mc68hc05jb4p Freescale Semiconductor, Inc, mc68hc05jb4p Datasheet - Page 72

• Manufacturer Part Number: mc68hc05jb4p
• Description: Mc68hc705jb4 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
10.2.1.4 Endpoint Field (ENDP)
10.2.1.5 Cyclic Redundancy Check (CRC)
Data Stream
The Endpoint field is a four bit number that is used to select a particular endpoint
within a USB device. For the MC68HC05JB4, this will be a binary number
between zero and two inclusive. Any other value will cause the transaction to be
ignored.
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 sixteen 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. Figure 10-6 shows how the
five bit CRC value is calculated from the data stream and verified for the address
and endpoint fields of a token packet. Figure 10-7 shows how the sixteen bit CRC
value is calculated and either transmitted or verified for the data packet of a given
transaction.
Figure 10-6. CRC Block Diagram for Address and Endpoint Fields
- Update every bit time.
- Reset to ones at SOP
next bit
Freescale Semiconductor, Inc.
For More Information On This Product,
UNIVERSAL SERIAL BUS MODULE
0
Go to: www.freescale.com
5
MUX
February 24, 1999
5
5
1
Generator Polynomial:
Good CRC
0
0 0 1 0 1
5
Y
Equal?
Expected Residual:
N
0 1 1 0 0
5
Bad CRC
REV