C8051T322-GQR Silicon Labs, C8051T322-GQR Datasheet - Page 258

• Manufacturer Part Number: C8051T322-GQR
• Description: 8-bit Microcontrollers - MCU USB-OTP-16K-LQFP32
• Manufacturer: Silicon Labs

Specifications of C8051T322-GQR

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

C8051T620/621/320/321/322/323
28.3.3. Low-Frequency Oscillator (LFO) Capture Mode
The Low-Frequency Oscillator Capture Mode allows the LFO clock to be measured against the system
clock or an external oscillator source. Timer 3 can be clocked from the system clock, the system clock
divided by 12, or the external oscillator divided by 8, depending on the T3ML (CKCON.6), and
T3XCLK[1:0] settings.
Setting TF3CEN to 1 enables the LFO Capture Mode for Timer 3. In this mode, T3SPLIT should be set to
0, as the full 16-bit timer is used. Upon a falling edge of the low-frequency oscillator, the contents of
Timer 3 (TMR3H:TMR3L) are loaded into the Timer 3 reload registers (TMR3RLH:TMR3RLL) and the
TF3H flag is set. By recording the difference between two successive timer capture values, the LFO clock
frequency can be determined with respect to the Timer 3 clock. The Timer 3 clock should be much faster
than the LFO to achieve an accurate reading. This means that the LFO/8 should not be selected as the
timer clock source in this mode.
258
External Clock / 8
SYSCLK / 12
Figure 28.9. Timer 3 Low-Frequency Oscillation Capture Mode Block Diagram
Low-Frequency
SYSCLK
Oscillator
T3XCLK[1:0]
00
01
M
H
T
3
M
T
3
L
0
1
CKCON
M
H
T
2
M
T
2
L
M
T
1
TF3CEN
M
T
0
S
C
A
1
TR3
S
C
A
0
Rev. 1.1
Capture
TCLK
TMR3RLL TMR3RLH
TMR3L
TMR3H
T3XCLK1
T3XCLK0
TF3CEN
T3SPLIT
TF3LEN
TF3H
TF3L
TR3
Interrupt