P89CV51RB2_09 datasheet(39/76 Pages) NXP

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P89CV51RB2_RC2_RD2_3

Product data sheet

Rev. 03 — 25 August 2009

39 of 76

NXP Semiconductors

P89CV51RB2/RC2/RD2

80C51 with 1 kB RAM, SPI

SM2 has no effect in Mode 0, and in Mode 1 can be used to check the validity of the stop

bit, although it is preferable to use the Framing Error ﬂag (FE). When the UART receives

data in Mode 1 and SM2 = 1, the receive interrupt will not be activated unless a valid stop

bit is received.

6.6.9 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 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 1 to 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 the SADDR to create the given

address which the master will use for addressing each of the slaves. Use of the given

address allows multiple slaves to be recognized while excluding others.

This device uses the methods presented in Figure 15 to determine if a given or broadcast

address has been received or not.

Fig 15. Schemes used by the UART to detect ‘given’ and ‘broadcast’ addresses when

multiprocessor communications is enabled

002aaa527

rx_byte(7)

saddr(7)

saden(7)

rx_byte(0)

saddr(0)

given_address_match

logic used by UART to detect 'given address' in received data

saddr(7)

saden(7)

rx_byte(7)

saddr(0)

saden(0)

rx_byte(0)

broadcast_address_match

logic used by UART to detect 'given address' in received data

saden(0)

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