TS80C52X2
:12
0
1
XTAL1
F
F
OSC
XTAL
T2
TR2
C/T2
T2CONreg
T2CONreg
(DOWN COUNTING RELOAD VALUE)
T2EX:
if DCEN=1, 1=UP
if DCEN=1, 0=DOWN
if DCEN = 0, up counting
FFh
(8-bit)
FFh
(8-bit)
T2CONreg
EXF2
TOGGLE
TL2
(8-bit)
TH2
(8-bit)
TIMER 2
INTERRUPT
TF2
T2CONreg
RCAP2L
(8-bit)
RCAP2H
(8-bit)
(UP COUNTING RELOAD VALUE)
Figure 4. Auto-Reload Mode Up/Down Counter (DCEN = 1)
6.3.2 Programmable Clock-Output
In the clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock generator (See Figure 5) . The
input clock increments TL2 at frequency F /2. The timer repeatedly counts to overflow from a loaded value.
OSC
At overflow, the contents of RCAP2H and RCAP2L registers are loaded into TH2 and TL2. In this mode, timer
2 overflows do not generate interrupts. The formula gives the clock-out frequency as a function of the system
oscillator frequency and the value in the RCAP2H and RCAP2L registers :
F
osc
Clock – OutFrequency = --------------------------------------------------------------------------------------
4 × (65536 – RCAP2H ⁄ RCAP2L)
For a 16 MHz system clock, timer 2 has a programmable frequency range of 61 Hz
16)
(F
/2 to 4 MHz (F
/4). The generated clock signal is brought out to T2 pin (P1.0).
OSC
OSC
Timer 2 is programmed for the clock-out mode as follows:
● Set T2OE bit in T2MOD register.
● Clear C/T2 bit in T2CON register.
● Determine the 16-bit reload value from the formula and enter it in RCAP2H/RCAP2L registers.
● Enter a 16-bit initial value in timer registers TH2/TL2. It can be the same as the reload value or a different
one depending on the application.
14
Rev. B - Jan. 25, 1999
Preliminary
TEMIC [ TEMIC SEMICONDUCTORS ]
