C8051F310/1/2/3/4/5/6/7
17.2. Timer 2
Timer 2 is a 16-bit timer formed by two 8-bit SFRs: TMR2L (low byte) and TMR2H (high byte). Timer 2 may
operate in 16-bit auto-reload mode or (split) 8-bit auto-reload mode. The T2SPLIT bit (TMR2CN.3) defines
the Timer 2 operation mode.
Timer 2 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 2 (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.
17.2.1. 16-bit Timer with Auto-Reload
When T2SPLIT (TMR2CN.3) is zero, Timer 2 operates as a 16-bit timer with auto-reload. Timer 2 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 2
reload registers (TMR2RLH and TMR2RLL) is loaded into the Timer 2 register as shown in Figure 17.4,
and the Timer 2 High Byte Overflow Flag (TMR2CN.7) is set. If Timer 2 interrupts are enabled (if IE.5 is
set), an interrupt will be generated on each Timer 2 overflow. Additionally, if Timer 2 interrupts are enabled
and the TF2LEN bit is set (TMR2CN.5), an interrupt will be generated each time the lower 8 bits (TMR2L)
overflow from 0xFF to 0x00.
CKCON
T2XCLK
T
T
T
T
T
T
S
3
3
2
2
1
0
C
M
M
M
M
M
M
A
H
L
H
L
1
S
C
A
0
To SMBus
SYSCLK / 12
0
0
TR2
TMR2L
Overflow
To ADC,
SMBus
TCLK
External Clock / 8
SYSCLK
1
TMR2CN
1
TMR2L
TMR2H
TF2H
TF2L
TF2LEN
Interrupt
T2SPLIT
TR2
T2XCLK
TMR2RLL TMR2RLH
Reload
Figure 17.4. Timer 2 16-Bit Mode Block Diagram
Rev. 1.7
195
SILABS [ SILICON LABORATORIES ]
