Mode 3: Two 8-bit Counter/Timers (Timer 0 Only)
In Mode 3, Timer 0 is configured as two separate 8-bit counter/timers held in TL0 and TH0. The counter/timer in TL0 is controlled using
the Timer 0 control/status bits in TCON and TMOD: TR0, CT0, GATE0, and TF0. TL0 can use either the system clock or an external
input signal as its timebase. The TH0 register is restricted to a timer function sourced by the system clock or prescaled clock. TH0 is
enabled using the Timer 1 run control bit TR1. TH0 sets the Timer 1 overflow flag TF1 on overflow and thus controls the Timer 1 inter-
rupt.
The overflow rate for Timer 0 Low in 8-bit mode is:
F
TIMER0
=
F
Input Clock
2
8
– TL0
=
F
Input Clock
256 – TL0
The overflow rate for Timer 0 High in 8-bit mode is:
F
TIMER0
=
F
Input Clock
2
8
– TH0
=
F
Input Clock
256 – TH0
Timer 1 is inactive in Mode 3. When Timer 0 is operating in Mode 3, Timer 1 can be operated in Modes 0, 1 or 2, but cannot be clocked
by external signals nor set the TF1 flag and generate an interrupt. However, the Timer 1 overflow can be used to generate baud rates
for the SMBus and/or UART, and/or initiate ADC conversions. While Timer 0 is operating in Mode 3, Timer 1 run control is handled
through its mode settings. To run Timer 1 while Timer 0 is in Mode 3, set the Timer 1 Mode as 0, 1, or 2. To disable Timer 1, configure
it for Mode 3.
TCLK
TR0
0
1
0
1
SYSCLK
Pre-scaled Clock
GATE0
IN0PL
XOR
T0M
T0
INT0
CT0
TR1
TL0
(8 bits)
TF0
(Interrupt Flag)
TH0
(8 bits)
TF1
(Interrupt Flag)
Figure 19.3. T0 Mode 3 Block Diagram
19.3.3 Timer 2, Timer 3, Timer 4, and Timer 5
Timer 2, Timer 3, Timer 4, and Timer 5 are functionally equivalent, with the only differences being the top-level connections to other
parts of the system.
The timers are 16 bits wide, formed by two 8-bit SFRs: TMRnL (low byte) and TMRnH (high byte). Each timer may operate in 16-bit
auto-reload mode, dual 8-bit auto-reload (split) mode, or capture mode.
EFM8UB3 Reference Manual
Timers (Timer0, Timer1, Timer2, Timer3, Timer4, and Timer5)
silabs.com
| Building a more connected world.
Rev. 0.2 | 262