AT89C5132
generator and its calculation formula. The USB controller clock frequency must always be 48
MHz.
Figure 15-3. USB Clock Generator and Symbol
USBCLK
USB
CLOCK
PLL
CLOCK
USBCD1:0
48 MHz USB Clock
PLLclk
USBCD + 1
USB Clock Symbol
USBclk = --------------------------------
15.1.2
Serial Interface Engine (SIE)
The SIE performs the following functions:
•
•
•
•
•
•
•
NRZI data encoding and decoding
Bit stuffing and unstuffing
CRC generation and checking
ACKs and NACKs automatic generation
TOKEN type identifying
Address checking
Clock recovery (using DPLL)
Figure 15-4. SIE Block Diagram
End of Packet
Detector
SYNC Detector
PID Decoder
Start of Packet
Detector
NRZI ‘ NRZ
Bit Unstuffing
Packet Bit Counter
Address Decoder
Serial to Parallel
Converter
D+
D-
8
Data Out
Clock
Recover
SysClk
(12 MHz)
USB
CLOCK
48 MHz
CRC5 & CRC16
Generator/Check
USB Pattern Generator
Parallel to Serial Converter
Bit Stuffing
8
Data In
NRZI Converter
CRC16 Generator
69
4173E–USB–09/07
ATMEL [ ATMEL ]
