AT87C54X2-3CSUL View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT87C54X2-3CSUL

8-bit CMOS Microcontroller 16/32 Kbytes ROM/OTP

Atmel Corporation 

Figure 8-1. Auto-Reload Mode Up/Down Counter (DCEN = 1)

AT/TS8xC54/8X2

XTAL1

FXTAL

FOSC

(:6 in X2 mode)

:12

0

1

T2

C/T2

TR2

T2CONreg T2CONreg

(DOWN COUNTING RELOAD VALUE)

FFh FFh

(8-bit) (8-bit)

TL2 TH2

(8-bit) (8-bit)

T2EX:

if DCEN=1, 1=UP

if DCEN=1, 0=DOWN

TOG-

T2CONreg

EXF2

TF2

TIMER 2

INTERRUPT

T2CONreg

8.1.1

RCAP2L RCAP2H

(8-bit) (8-bit)

(UP COUNTING RELOAD VALUE)

Programmable Clock-Output

In the clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock generator

(See Figure 8-2) . The input clock increments TL2 at frequency FOSC/2. The timer repeatedly

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 :

Clock – OutFrequency

=

Fosc

RCAP H RC AP L 4-----×-----(---6---5---5---3----6-----–---------------------2---------⁄-------------------2-------)-

For a 16 MHz system clock, timer 2 has a programmable frequency range of 61 Hz

(FOSC/216) to 4 MHz (FOSC/4). The generated clock signal is brought out to T2 pin (P1.0).

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.

15

4431E–8051–04/06

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