C8051F344 View Datasheet(PDF) - Silicon Laboratories

Part Name

Description

MFG CO.

C8051F344

Full Speed USB Flash MCU Family

Silicon Laboratories 

C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D

21.3.3. USB Start-of-Frame Capture

When T3CE = ‘1’, Timer 3 will operate in one of two special capture modes. The capture event can be

selected between a USB Start-of-Frame (SOF) capture, and a Low-Frequency Oscillator (LFO) Rising

Edge capture, using the T3CSS bit. The USB SOF capture mode can be used to calibrate the system clock

or external oscillator against the known USB host SOF clock. The LFO rising-edge capture mode can be

used to calibrate the internal Low-Frequency Oscillator against the internal High-Frequency Oscillator or

an external clock source. When T3SPLIT = ‘0’, Timer 3 counts up and overflows from 0xFFFF to 0x0000.

Each time a capture event is received, the contents of the Timer 3 registers (TMR3H:TMR3L) are latched

into the Timer 3 Reload registers (TMR3RLH:TMR3RLL). A Timer 3 interrupt is generated if enabled.

TMR3CN

TTTTTTTT

FFF 3 3R3 3

3 3 3CS3CX

HL LEP SC

E L SL

NI K

T

SYSCLK / 12

0

External Clock / 8

1

SYSCLK

CKCON

TTTTTTSS

3 3 2 2 1 0CC

MMMMMMA A

HLHL 10

0

TR3

1

TCLK TMR3L TMR3H

USB Start-of-Frame (SOF)

Low-Frequency Oscillator

Falling Edge

0

Capture

TMR3RLL TMR3RLH

1

T3CSS

Enable

Interrupt

Figure 21.10. Timer 3 Capture Mode (T3SPLIT = ‘0’)

To ADC

Rev. 1.3

251

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