AT83SND1CXXX-ROTIL datasheet(139/212 Pages) ATMEL

139 / 212 page

139

4109J–8051–10/06

AT8xC51SND1C

Notes:

1. These frequencies are achieved in X1 mode, F

PER = FOSC ÷ 2.

2. These frequencies are achieved in X2 mode, FPER = FOSC.

17.4.5

Baud Rate Selection (Mode 2)

In mode 2, the baud rate can only be programmed to 2 fixed values: 1/16 or 1/32 of the periph-

eral clock frequency.

As shown in Figure 17-14 the selection is done using SMOD1 bit in PCON register.

Figure 17-15 gives the baud rate calculation formula depending on the selection.

Figure 17-14. Baud Rate Generator Selection (Mode 2)

Figure 17-15. Baud Rate Formula (Mode 2)

17.5

Multiprocessor Communication (Modes 2 and 3)

Modes 2 and 3 provide a ninth-bit mode to facilitate multiprocessor communication. To enable

this feature, set SM2 bit in SCON register. When the multiprocessor communication feature is

enabled, the serial Port can differentiate between data frames (ninth bit clear) and address

frames (ninth bit set). This allows the AT8xC51SND1C to function as a slave processor in an

environment where multiple slave processors share a single serial line.

When the multiprocessor communication feature is enabled, the receiver ignores frames with

the ninth bit clear. The receiver examines frames with the ninth bit set for an address match. If

the received address matches the slaves address, the receiver hardware sets RB8 and RI bits in

SCON register, generating an interrupt.

The addressed slave’s software then clears SM2 bit in SCON register and prepares to receive

the data Bytes. The other slaves are unaffected by these data Bytes because they are waiting to

respond to their own addresses.

9600

178

0.16

152

0.16

126

0.16

4800

100

0.16

126

0.16

Baud Rate

PER = 12 MHz

(2)

PER = 16 MHz

(2)

PER = 20 MHz

(2)

SPD

SMOD1

BRL

Error %

SPD

SMOD1

BRL

Error %

SPD

SMOD1

BRL

Error %

SMOD1

PCON.7

PER

CLOCK

÷ 2

÷ 16

To Serial Port

Baud_Rate=

SMOD1

⋅ F

PER

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