TS87C51RD2 ATMEL Corporation, TS87C51RD2 Datasheet - Page 20

• Manufacturer Part Number: TS87C51RD2
• Description: (TS8xC51Rx2) High Performance 8-bit Microcontroller
• Manufacturer: ATMEL Corporation

Figure 6-2.
6.2.2
20
AT/TS8xC51Rx2
Programmable Clock-Output
Auto-reload Mode Up/Down Counter (DCEN = 1)
XTAL1
In the clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock generator
(See Figure 6-3) . The input clock increments TL2 at frequency F
counts to overflow from a loaded value. At overflow, the contents of RCAP2H and RCAP2L reg-
isters 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:
For a 16 MHz system clock, timer 2 has a programmable frequency range of 61 Hz
(F
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
• Enter a 16-bit initial value in timer registers TH2/TL2. It can be the same as the reload value
• To start the timer, set TR2 run control bit in T2CON register.
OSC
registers.
or a different one depending on the application.
F
XTAL
/2
16)
to 4 MHz (F
C l o c k O u t F r e q u e n c y
OSC
F
OSC
–
/4). The generated clock signal is brought out to T2 pin (P1.0).
(DOWN COUNTING RELOAD VALUE)
(:6 in X2 mode)
(UP COUNTING RELOAD VALUE)
RCAP2L
T2
(8-bit)
:12
(8-bit)
(8-bit)
TL2
FFh
=
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4
T2CONreg
RCAP2H
C/T2
(8-bit)
(8-bit)
×
TH2
(8-bit)
0
FFh
1
(
65536
T2CONreg
–
R C A P
TR2
F o s c
T2EX:
if DCEN=1, 1=UP
if DCEN=1, 0=DOWN
if DCEN = 0, up
counting
TOGGLE
2
T2CONreg
H
OSC
TF2
⁄
R C A P
/2. The timer repeatedly
T2CONreg
EXF2
2
INTERRUPT
L
TIMER 2
)
4188E–8051–08/06