AT89C51CC01_14 Datasheet, PDF (66/167 Pages) ATMEL Corporation – Boot Code Section with Independent Lock Bits

Timer 2
The T89C51CC01 timer 2 is compatible with timer 2 in the 80C52.
It is a 16-bit timer/counter: the count is maintained by two eight-bit timer registers, TH2
and TL2 that are cascade- connected. It is controlled by T2CON register (See Table )
and T2MOD register (See Table 48). Timer 2 operation is similar to Timer 0 and Timer
1. C/T2 selects F_{T2 clock}/6 (timer operation) or external pin T2 (counter operation) as
timer clock. Setting TR2 allows TL2 to be incremented by the selected input.
Timer 2 includes the following enhancements:
• Auto-reload mode (up or down counter)
• Programmable clock-output
Auto-Reload Mode
The auto-reload mode configures timer 2 as a 16-bit timer or event counter with auto-
matic reload. This feature is controlled by the DCEN bit in T2MOD register (See
Table 48). Setting the DCEN bit enables timer 2 to count up or down as shown in
Figure 36. In this mode the T2EX pin controls the counting direction.
When T2EX is high, timer 2 counts up. Timer overflow occurs at FFFFh which sets the
TF2 flag and generates an interrupt request. The overflow also causes the 16-bit value
in RCAP2H and RCAP2L registers to be loaded into the timer registers TH2 and TL2.
When T2EX is low, timer 2 counts down. Timer underflow occurs when the count in the
timer registers TH2 and TL2 equals the value stored in RCAP2H and RCAP2L registers.
The underflow sets TF2 flag and reloads FFFFh into the timer registers.
The EXF2 bit toggles when timer 2 overflow or underflow, depending on the direction of
the count. EXF2 does not generate an interrupt. This bit can be used to provide 17-bit
resolution.
Figure 36. Auto-Reload Mode Up/Down Counter
see section “Clock”
FT2
:6
CLOCK
T2
0
1
CT/2
T2CON.1
TR2
T2CON.2
(DOWN COUNTING RELOAD VALUE)
FFh FFh
(8-bit) (8-bit)
T2EX:
1=UP
2=DOWN
TL2
(8-bit)
TH2
(8-bit)
TOGGLE T2CONreg
EXF2
TF2
TIMER 2
INTERRUPT
T2CONreg
66 A/T89C51CC01
RCAP2L RCAP2H
(8-bit)
(8-bit)
(UP COUNTING RELOAD VALUE)
4129N–CAN–03/08