P87C552 datasheet(13/74 Pages) PHILIPS

13 / 74 page

Philips Semiconductors

Preliminary specification

P87C552

80C51 8-bit microcontroller

8K/256 OTP, 8 channel 10 bit A/D, I2C, PWM,

capture/compare, high I/O, low voltage (2.7V–5.5V), low power

1999 Mar 30

Enhanced UART

The UART operates in all of the usual modes that are described in

the first section of

Data Handbook IC20, 80C51-Based 8-Bit

Microcontrollers. In addition the UART can perform framing error

detect by looking for missing stop bits, and automatic address

recognition. The UART also fully supports multiprocessor

communication as does the standard 80C51 UART.

When used for framing error detect the UART looks for missing stop

bits in the communication. A missing bit will set the FE bit in the

S0CON register. The FE bit shares the S0CON.7 bit with SM0 and

the function of S0CON.7 is determined by PCON.6 (SMOD0) (see

Figure 7). If SMOD0 is set then S0CON.7 functions as FE.

S0CON.7 functions as SM0 when SMOD0 is cleared. When used as

FE S0CON.7 can only be cleared by software. Refer to Figure 8.

Automatic Address Recognition

Automatic Address Recognition is a feature which allows the UART

to recognize certain addresses in the serial bit stream by using

hardware to make the comparisons. This feature saves a great deal

of software overhead by eliminating the need for the software to

examine every serial address which passes by the serial port. This

feature is enabled by setting the SM2 bit in S0CON. In the 9 bit

UART modes, mode 2 and mode 3, the Receive Interrupt flag (RI)

will be automatically set when the received byte contains either the

“Given” address or the “Broadcast” address. The 9 bit mode

requires that the 9th information bit is a 1 to indicate that the

received information is an address and not data. Automatic address

recognition is shown in Figure 9.

The 8 bit mode is called Mode 1. In this mode the RI flag will be set

if SM2 is enabled and the information received has a valid stop bit

following the 8 address bits and the information is either a Given or

Broadcast address.

S0CON Address = 98H

Reset Value = 0000 0000B

SM0/FE

SM1

SM2

REN

TB8

RB8

Bit Addressable

(SMOD0 = 0/1)*

Symbol

Function

Framing Error bit. This bit is set by the receiver when an invalid stop bit is detected. The FE bit is not cleared by valid

frames but should be cleared by software. The SMOD0 bit must be set to enable access to the FE bit.

SM0

Serial Port Mode Bit 0, (SMOD0 must = 0 to access bit SM0)

SM1

Serial Port Mode Bit 1

SM0

SM1

Mode

Description

Baud Rate**

shift register

fOSC/12

8-bit UART

variable

9-bit UART

fOSC/64 or fOSC/32

9-bit UART

variable

SM2

Enables the Automatic Address Recognition feature in Modes 2 or 3. If SM2 = 1 then Rl will not be set unless the

received 9th data bit (RB8) is 1, indicating an address, and the received byte is a Given or Broadcast Address.

In Mode 1, if SM2 = 1 then Rl will not be activated unless a valid stop bit was received, and the received byte is a

Given or Broadcast Address. In Mode 0, SM2 should be 0.

REN

Enables serial reception. Set by software to enable reception. Clear by software to disable reception.

TB8

The 9th data bit that will be transmitted in Modes 2 and 3. Set or clear by software as desired.

RB8

In modes 2 and 3, the 9th data bit that was received. In Mode 1, if SM2 = 0, RB8 is the stop bit that was received.

In Mode 0, RB8 is not used.

Transmit interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or at the beginning of the stop bit in the

other modes, in any serial transmission. Must be cleared by software.

Receive interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or halfway through the stop bit time in

the other modes, in any serial reception (except see SM2). Must be cleared by software.

NOTE:

*SMOD0 is located at PCON6.

**fOSC = oscillator frequency

SU00981

Bit:

7654

321

Figure 7. S0CON: Serial Port Control Register

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