DS87C550 datasheet(21/49 Pages) MAXIM

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DS87C550 EPROM High-Speed Microcontroller with ADC and PWM

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EMI REDUCTION

One of the major contributors to radiated noise in an 8051-based system is the toggling of ALE. The

DS87C550 allows software to disable ALE when not used by setting the ALEOFF (PMR.2) bit to a 1.

When ALEOFF = 1, ALE will still toggle during an off-chip MOVX. However, ALE will remain inactive

when performing on-chip memory access. The default state is ALEOFF = 0 so ALE normally toggles at a

frequency of XTAL/4.

PERIPHERAL OVERVIEW

The DS87C550 provides several of the most commonly needed peripheral functions in microcomputer-

based systems. New functions include a second serial port, power-fail reset, power-fail interrupt flag, and

a programmable watchdog timer. In addition, the DS87C550 contains an analog-to-digital converter and

four channels of pulse width modulation for industrial control and measurement applications. Each of

these peripherals is described below. More details are available in the High-Speed Microcontroller User's

Guide: DS87C550 Supplement.

SERIAL PORTS

The DS87C550 provides a serial port (UART) that is identical to the 80C52. In addition, it includes a

second hardware serial port that is a full duplicate of the standard one. This port optionally uses pins P1.6

(RXD1) and P1.7 (TXD1). It has duplicate control functions included in new SFR locations.

Both ports can operate simultaneously but can be at different baud rates or even in different modes. The

second serial port has similar control registers (SCON1, SBUF1) to the original. The new serial port can

only use Timer 1 for timer generated baud rates.

Control for serial port 0 is provided by the SCON0 register while its I/O buffer is SBUF0. The registers

SCON1 and SBUF1 provide the same functions for the second serial port. A full description of the use

and operation of both serial ports may be found in the High-Speed Microcontroller User's Guide,

available from the Maxim website.

ANALOG TO DIGITAL CONVERTER

The DS87C550 contains a 10-bit successive approximation analog-to-digital converter. This converter

provides eight multiplexed channels of analog input using an external voltage reference for the

conversion process.

Before using the A/D converter, the converter must be configured by performing two actions:

1. The user must set the ADON bit (ADCON1.1). This enables the A/D converter. This bit defaults to 0

following a reset, disabling the A/D converter to conserve power.

2. In addition, the user must set the ADRS bit (PWMADR.7) to enable the external voltage reference

pins. This bit defaults to 0 following a reset, disabling the A/D converter voltage reference pins.

A/D CONVERTER INPUTS

The A/D converter of the DS87C550 provides eight channels of analog input on device pins ADC7

through ADC0 (P5.7-P5.0). The signals on these pins are input into an analog multiplexer. The magnitude

(and polarity) of these signals is limited by the external reference (AVREF+, AVREF-) voltages used by the

converter. See the DC electrical characteristics section of this data sheet for more details.

DS87C550 Datasheet(PDF) 21 Page - Maxim Integrated Products