T84C5112-RKFEL datasheet(7/97 Pages) ATMEL

7 / 97 page

Rev. B - November 10, 2000

Preliminary

T80C5112

6. Clock system

6.1. Overview

The T80C5112 oscillator system provides a reliable clocking system with full mastering of speed versus CPU

power trade off. Several clocks sources are possible:

· External clock input

· High speed crystal or ceramic oscillator

· Low speed crystal oscillator

· Integrated high speed RC oscillator

· The low speed RC oscillator of the watchdog is a backup clocking source when no clock are selected in active

or idle modes.

The selected clock source can be divided by 2-512 before clocking the CPU and the peripherals. When X2 function

is set, the CPU need 6 clock periods per cycle.

Active oscillator at reset is defined by bits in a configuration byte programmed on an OTP programmer or by

metal mask.

Clocking is controlled by several SFR registers : OSCON, CKCON0, CKCON1, CKRL.

6.2. Blocks description

The T80C5112 includes the following oscillators:

· Crystal oscillator, with two possible gains optimized for 32 kHz or 33 MHz.

· Integrated high speed RC oscillator, with typical frequency of 12 MHz

· Integrated low speed, low power RC oscillator, with typical frequency of 200 kHz; this oscillator is used to

clock the hardware watchdog and as back up oscillator when the CPU receives no clock signal in active or

idle modes.

6.2.1. Crystal oscillator : OSCA

The crystal oscillator uses two external pins, XTAL1 for input and XTAL2 for output.

XT_SP in configuration byte allows to select between two possible gains optimized for 32 kHz or 33 MHz. Both

crystal and ceramic resonnators can be used.

OSCAEN in OSCCON register is an enable signal for the crystal oscillator or the external oscillator input.

When the crystal oscillator is not selected, XTAL1 can be used as a standard C51 I/O port, and X2 can be used

as a standard C51 I/O port.

6.2.2. Integrated high speed RC oscillator : OSCB

The high speed RC oscillator do not need any external component; its typical frequency is 12 MHz. Note that the

on chip oscillator has a +-25% frequency tolerance and for that reason may not be suitable for use in some applications.

OSCBEN in OSCCON register is an enable signal for the high speed RC oscillator.

T84C5112-RKFEL 데이터시트(PDF) 7 Page - ATMEL Corporation