C8051F581-IMR Silicon Labs, C8051F581-IMR Datasheet - Page 299

• Manufacturer Part Number: C8051F581-IMR
• Description: 8-bit Microcontrollers - MCU 50MIPS 128kB 8kB SPI
• Manufacturer: Silicon Labs

Specifications of C8051F581-IMR

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

27.3. Timer 3
Timer 3 is a 16-bit timer formed by two 8-bit SFRs: TMR3L (low byte) and TMR3H (high byte). Timer 3 may
operate in 16-bit auto-reload mode or (split) 8-bit auto-reload mode. The T3SPLIT bit (TMR3CN.3) defines
the Timer 3 operation mode.
Timer 3 may be clocked by the system clock, the system clock divided by 12, or the external oscillator
source divided by 8. The external clock mode is ideal for real-time clock (RTC) functionality, where the
internal oscillator drives the system clock while Timer 3 (and/or the PCA) is clocked by an external preci-
sion oscillator. Note that the external oscillator source divided by 8 is synchronized with the system clock.
27.3.1. 16-bit Timer with Auto-Reload
When T3SPLIT (TMR3CN.3) is zero, Timer 3 operates as a 16-bit timer with auto-reload. Timer 3 can be
clocked by SYSCLK, SYSCLK divided by 12, or the external oscillator clock source divided by 8. As the
16-bit timer register increments and overflows from 0xFFFF to 0x0000, the 16-bit value in the Timer 3
reload registers (TMR3RLH and TMR3RLL) is loaded into the Timer 3 register as shown in Figure 27.7,
and the Timer 3 High Byte Overflow Flag (TMR3CN.7) is set. If Timer 3 interrupts are enabled, an interrupt
will be generated on each Timer 3 overflow. Additionally, if Timer 3 interrupts are enabled and the TF3LEN
bit is set (TMR3CN.5), an interrupt will be generated each time the lower 8 bits (TMR3L) overflow from
0xFF to 0x00.
27.3.2. 8-bit Timers with Auto-Reload
When T3SPLIT is set, Timer 3 operates as two 8-bit timers (TMR3H and TMR3L). Both 8-bit timers oper-
ate in auto-reload mode as shown in Figure 27.8. TMR3RLL holds the reload value for TMR3L; TMR3RLH
holds the reload value for TMR3H. The TR3 bit in TMR3CN handles the run control for TMR3H. TMR3L is
always running when configured for 8-bit Mode.
Each 8-bit timer may be configured to use SYSCLK, SYSCLK divided by 12, or the external oscillator clock
source divided by 8. The Timer 3 Clock Select bits (T3MH and T3ML in CKCON) select either SYSCLK or
the clock defined by the Timer 3 External Clock Select bit (T3XCLK in TMR3CN), as follows:
External Clock / 8
T3MH
SYSCLK / 12
0
0
1
SYSCLK
T3XCLK
T3XCLK
0
1
X
0
1
M
H
T
3
T
M
Figure 27.7. Timer 3 16-Bit Mode Block Diagram
3
L
SYSCLK/12
External Clock/8
SYSCLK
TMR3H Clock Source
CKCON
M
T
2
H
M
T
2
L
0
1
M
T
1
T
M
0
S
C
A
1
C
S
A
0
TR3
TCLK
Rev. 1.2
Overflow
TL3
TMR3RLL TMR3RLH
TMR3L
To SMBus
T3ML
TMR3H
0
0
1
Reload
C8051F58x/F59x
T3XCLK
To ADC,
X
SMBus
0
1
T3SPLIT
TF3CEN
T3XCLK
TF3LEN
TF3H
TF3L
TR3
SYSCLK/12
External Clock/8
SYSCLK
TMR3L Clock Source
Interrupt
299