C8051F93X Datasheet, PDF (299/330 Pages) Silicon Laboratories – Pipelined intstruction architecture executes 70 of instruction in 1 or 2 system clocks

C8051F93x-C8051F92x
25.3. 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 (TMR2CN.3) defines
the Timer 3 operation mode. Timer 3 can also be used in Capture Mode to measure the external oscillator
source or the Comparator 1 period with respect to another oscillator. The ability to measure the
Comparator 1 period with respect to the system clock is makes using Touch Sense Switches very easy.
Timer 3 may be clocked by the system clock, the system clock divided by 12, external oscillator source
divided by 8, or Comparator 1 output. The external oscillator source divided by 8 and Comparator 1 output
is synchronized with the system clock.
25.3.1. 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, external oscillator clock source divided by 8, or Comparator 1
output. 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 25.7, and the Timer 3 High Byte Overflow Flag (TMR3CN.7) is set. If Timer 3 interrupts are enabled
(if EIE1.7 is set), 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.
T3XCLK[1:0]
SYSCLK / 12
00
External Clock / 8
01
SYSCLK / 12
10
Comparator 1
11
CKCON
TTTTTTSS
3 3 2 2 1 0CC
MMMMMMA A
HLHL 10
0
TR3
1
SYSCLK
To ADC
TCLK
TMR3L
TMR3H
TMR3RLL TMR3RLH
Reload
TF3H
TF3L
TF3LEN
TF3CEN
T3SPLIT
TR3
T3XCLK1
T3XCLK0
Interrupt
Figure 25.7. Timer 3 16-Bit Mode Block Diagram
Rev. 1.3
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