Rev. B - Jan. 25, 1999

19

Preliminary

TS80C52X2

Software may examine FE bit after each reception to check for data errors. Once set, only software or a reset can

clear FE bit. Subsequently received frames with valid stop bits cannot clear FE bit. When FE feature is enabled,

RI rises on stop bit instead of the last data bit (See Figure 7. and Figure 8.).

Figure 7. UART Timings in Mode 1

Figure 8. UART Timings in Modes 2 and 3

6.4.2 Automatic Address Recognition

The automatic address recognition feature is enabled when the multiprocessor communication feature is enabled

(SM2 bit in SCON register is set).

Implemented in hardware, automatic address recognition enhances the multiprocessor communication feature by

allowing the serial port to examine the address of each incoming command frame. Only when the serial port

recognizes its own address, the receiver sets RI bit in SCON register to generate an interrupt. This ensures that

the CPU is not interrupted by command frames addressed to other devices.

If desired, you may enable the automatic address recognition feature in mode 1. In this configuration, the stop bit

takes the place of the ninth data bit. Bit RI is set only when the received command frame address matches the

device’s address and is terminated by a valid stop bit.

To support automatic address recognition, a device is identified by a given address and a broadcast address.

NOTE: The multiprocessor communication and automatic address recognition features cannot be enabled in mode 0 (i.e. setting SM2 bit in SCON

register in mode 0 has no effect).

Data byte

RI

SMOD0=X

Stop

bit

Start

bit

RXD

D7

D6

D5

D4

D3

D2

D1

D0

FE

SMOD0=1

RI

SMOD0=0

Data byte

Ninth

bit

Stop

bit

Start

bit

RXD

D8

D7

D6

D5

D4

D3

D2

D1

D0

RI

SMOD0=1

FE

SMOD0=1