C8051F320-TB Silicon Laboratories Inc, C8051F320-TB Datasheet - Page 146

• Manufacturer Part Number: C8051F320-TB
• Description: BOARD PROTOTYPING W/C8051F320
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F320-TB

• Contents: Board
• Processor To Be Evaluated: C8051F320/F321
• Interface Type: USB
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F320
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

C8051F320/1
15.4. USB Clock Configuration
USB0 is capable of communication as a Full or Low Speed USB function. Communication speed is
selected via the SPEED bit in SFR USB0XCN. When operating as a Low Speed function, the USB0 clock
must be 6 MHz. When operating as a Full Speed function, the USB0 clock must be 48 MHz. Clock options
are described in Section “13. Oscillators” on page 116. The USB0 clock is selected via SFR CLKSEL (see
Figure 13.5 on Page 124).
Clock Recovery circuitry uses the incoming USB data stream to adjust the internal oscillator; this allows
the internal oscillator (and 4x Clock Multiplier) to meet the requirements for USB clock tolerance. Clock
Recovery should be used in the following configurations:
When operating USB0 as a Low Speed function with Clock Recovery, software must write ‘1’ to the
CRLOW bit to enable Low Speed Clock Recovery. Clock Recovery is typically not necessary in Low Speed
mode.
Single Step Mode can be used to help the Clock Recovery circuitry to lock when high noise levels are pres-
ent on the USB network. This mode is not required (or recommended) in typical USB environments.
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Bit7:
Bit6:
Bit5:
Bits4–0: Reserved. Read = Variable. Must Write = 1001b.
CRE
R/W
Bit7
Full Speed
Low Speed
USB Register Definition 15.5. CLKREC: Clock Recovery Control
CRE: Clock Recovery Enable.
This bit enables/disables the USB clock recovery feature.
0: Clock recovery disabled.
1: Clock recovery enabled.
CRSSEN: Clock Recovery Single Step.
This bit forces the oscillator calibration into ‘single-step’ mode during clock recovery.
0: Normal calibration mode.
1: Single step mode.
CRLOW: Low Speed Clock Recovery Mode.
This bit must be set to ‘1’ if clock recovery is used when operating as a Low Speed USB
device.
0: Full Speed Mode.
1: Low Speed Mode.
Communication Speed
CRSSEN
R/W
Bit6
CRLOW
R/W
Bit5
4x Clock Multiplier
Internal Oscillator/2
R/W
Bit4
USB Clock
Rev. 1.4
R/W
Bit3
Reserved
R/W
Bit2
Internal Oscillator
N/A
4x Clock Multiplier Input
R/W
Bit1
R/W
Bit0
USB Address:
00001001
Reset Value
0x0F