C8051F540-TB Silicon Laboratories Inc, C8051F540-TB Datasheet - Page 238

BOARD PROTOTYPE W/C8051F540

C8051F540-TB

Manufacturer Part Number
C8051F540-TB
Description
BOARD PROTOTYPE W/C8051F540
Manufacturer
Silicon Laboratories Inc
Type
MCUr
Datasheets

Specifications of C8051F540-TB

Contents
Board
Processor To Be Evaluated
C8051F54x
Processor Series
C8051F54x
Interface Type
USB
Operating Supply Voltage
5 V
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
For Use With/related Products
C8051F54x
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
Other names
336-1672
C8051F54x
The TF2H bit is set when TMR2H overflows from 0xFF to 0x00; the TF2L bit is set when TMR2L overflows
from 0xFF to 0x00. When Timer 2 interrupts are enabled (IE.5), an interrupt is generated each time
TMR2H overflows. If Timer 2 interrupts are enabled and TF2LEN (TMR2CN.5) is set, an interrupt is gener-
ated each time either TMR2L or TMR2H overflows. When TF2LEN is enabled, software must check the
TF2H and TF2L flags to determine the source of the Timer 2 interrupt. The TF2H and TF2L interrupt flags
are not cleared by hardware and must be manually cleared by software.
23.2.3. External Oscillator Capture Mode
Capture Mode allows the external oscillator to be measured against the system clock. Timer 2 can be
clocked from the system clock, or the system clock divided by 12, depending on the T2ML (CKCON.4),
and T2XCLK bits. When a capture event is generated, the contents of Timer 2 (TMR2H:TMR2L) are
loaded into the Timer 2 reload registers (TMR2RLH:TMR2RLL) and the TF2H flag is set. A capture event
is generated by the falling edge of the clock source being measured, which is the external oscillator / 8. By
recording the difference between two successive timer capture values, the external oscillator frequency
can be determined with respect to the Timer 2 clock. The Timer 2 clock should be much faster than the
capture clock to achieve an accurate reading. Timer 2 should be in 16-bit auto-reload mode when using
Capture Mode.
For example, if T2ML = 1b and TF2CEN = 1b, Timer 2 will clock every SYSCLK and capture every external
clock divided by 8. If the SYSCLK is 24 MHz and the difference between two successive captures is 5984,
then the external clock frequency is as follows:
24 MHz/(5984/8) = 0.032086 MHz or 32.086 kHz
238
External Clock / 8
T2MH
SYSCLK / 12
0
0
1
T2XCLK
T2XCLK
X
0
1
0
1
SYSCLK/12
External Clock/8
SYSCLK
TMR2H Clock Source
SYSCLK
Figure 23.5. Timer 2 8-Bit Mode Block Diagram
0
1
1
0
M
H
T
3
M
T
3
L
CKCON
M
H
T
2
M
T
2
L
M
T
1
T
M
0
TR2
S
C
A
1
S
C
A
0
Rev. 1.1
TCLK
TCLK
TMR2RLH
TMR2RLL
TMR2H
TMR2L
T2ML
0
0
1
Reload
Reload
T2XCLK
X
0
1
To SMBus
To ADC,
TF2CEN
T2SPLIT
TF2LEN
T2XCLK
SMBus
TF2H
TF2L
TR2
SYSCLK/12
External Clock/8
SYSCLK
TMR2L Clock Source
Interrupt

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