P89LV51RD2BA PHILIPS [NXP Semiconductors], P89LV51RD2BA Datasheet - Page 40

• Manufacturer Part Number: P89LV51RD2BA
• Description: 8-bit 80C51 3 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 14342
Product data
7.5.7 More about UART modes 2 and 3
7.5.8 Multiprocessor communications
7.5.9 Automatic address recognition
Reception is performed in the same manner as in mode 1.
The signal to load SBUF and RB8, and to set RI, will be generated if, and only if, the
following conditions are met at the time the final shift pulse is generated: (a) RI = 0,
and (b) Either SM2 = 0, or the received 9th data bit =
If either of these conditions is not met, the received frame is irretrievably lost, and RI
is not set. If both conditions are met, the received 9th data bit goes into RB8, and the
first 8 data bits go into SBUF.
UART modes 2 and 3 have a special provision for multiprocessor communications. In
these modes, 9 data bits are received or transmitted. When data is received, the 9th
bit is stored in RB8. The UART can be programmed so that when the stop bit is
received, the serial port interrupt will be activated only if RB8 =
enabled by setting bit SM2 in SCON. One way to use this feature in multiprocessor
systems is as follows:
When the master processor wants to transmit a block of data to one of several slaves,
it first sends out an address byte which identifies the target slave. An address byte
differs from a data byte in a way that the 9th bit is
data byte. With SM2 = 1, no slave will be interrupted by a data byte, i.e. the received
9th bit is ‘0’. However, an address byte having the 9th bit set to
slaves, so that each slave can examine the received byte and see if it is being
addressed or not. The addressed slave will clear its SM2 bit and prepare to receive
the data (still 9 bits long) that follow. The slaves that weren’t being addressed leave
their SM2 bits set and go on about their business, ignoring the subsequent data
bytes.
SM2 has no effect in Mode 0, and in Mode 1 can be used to check the validity of the
stop bit, although this is better done with the Framing Error flag. When UART receives
data in mode 1 and SM2 =
stop bit is received.
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 for the UART by setting the SM2 bit in SCON. 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
indicate that the received information is an address and not data.
Using the Automatic Address Recognition feature allows a master to selectively
communicate with one or more slaves by invoking the Given slave address or
addresses. All of the slaves may be contacted by using the Broadcast address. Two
Special Function Registers are used to define the slave’s address, SADDR, and the
address mask, SADEN. SADEN is used to define which bits in the SADDR are to be
used and which bits are ‘don’t care’. The SADEN mask can be logically ANDed with
Rev. 04 — 02 December 2004
1
, the receive interrupt will not be activated unless a valid
P89LV51RB2/RC2/RD2
8-bit microcontrollers with 80C51 core
‘1’
in an address byte and ‘0’ in the
1.
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
‘1’
1
. This feature is
will interrupt all
‘1’
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to