C8051F34A-GMR Silicon Labs, C8051F34A-GMR Datasheet - Page 166

• Manufacturer Part Number: C8051F34A-GMR
• Description: 8-bit Microcontrollers - MCU 48 MIPS 64KB 10ADC
• Manufacturer: Silicon Labs

Specifications of C8051F34A-GMR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D
16.4. 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
(see SFR Definition 14.6).
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.
166
Bit7:
Bit6:
Bit5:
Bits4–0: Reserved. Read = Variable. Must Write = 01001b.
Note: The USB transceiver must be enabled before enabling Clock Recovery.
CRE
Communication Speed
R/W
Bit7
Low Speed
USB Register Definition 16.5. 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.
Full Speed
CRSSEN
Section “14. Oscillators” on page 131
R/W
Bit6
CRLOW
R/W
Bit5
R/W
Bit4
Internal Oscillator / 2
4x Clock Multiplier
USB Clock
Rev. 1.3
R/W
Bit3
. The USB0 clock is selected via SFR CLKSEL
Reserved
R/W
Bit2
R/W
Bit1
4x Clock Multiplier Input
Internal Oscillator
R/W
Bit0
N/A
USB Address:
00001001
Reset Value
0x0F