AT89LP2052 datasheet(38/90 Pages) ATMEL

38 / 90 page

3547F–MICRO–6/06

AT89LP2052/LP4052

17.6

Framing Error Detection

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 SCON register. The FE bit shares the SCON.7 bit with SM0

and the function of SCON.7 is determined by PCON.6 (SMOD0). If SMOD0 is set then SCON.7

functions as FE. SCON.7 functions as SM0 when SMOD0 is cleared. When used as FE,

SCON.7 can only be cleared by software.

17.7

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 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 “Broad-

cast” 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.

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.

Mode 0 is the Shift Register mode and SM2 is ignored.

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. The following examples will help to show the versatility of this scheme:

Slave 0

SADDR = 1100 0000

SADEN = 1111 1101

Given

= 1100 00X0

Slave 1

SADDR = 1100 0000

SADEN = 1111 1110

Given

= 1100 000X

In the previous example SADDR is the same and the SADEN data is used to differentiate

between the two slaves. Slave 0 requires a “0” in bit 0 and it ignores bit 1. Slave 1 requires a “0”

in bit 1 and bit 0 is ignored. A unique address for slave 0 would be 1100 0010 since slave 1

requires a “0” in bit 1. A unique address for slave 1 would be 1100 0001 since a “1” in bit 0 will

exclude slave 0. Both slaves can be selected at the same time by an address which has bit 0 = 0

(for slave 0) and bit 1 = 0 (for slave 1). Thus, both could be addressed with 1100 0000.

In a more complex system the following could be used to select slaves 1 and 2 while excluding

slave 0:

AT89LP2052 датащи(PDF) 38 Page - ATMEL Corporation

AT89LP2052 датащи(HTML) 38 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

датащи скачать

ссылки URL