ST72P623 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST72P623

LOW SPEED USB 8-BIT MCU WITH 3 ENDPOINTS, FLASH OR ROM MEMORY, LVD, WDG, 10-BIT ADC, 2 TIMERS, SCI, SPI

STMicroelectronics 

ST7262xxx

SERIAL COMMUNICATIONS INTERFACE (Cont’d)

Framing Error

A framing error is detected when:

– The stop bit is not recognized on reception at the

expected time, following either a de-synchroni-

zation or excessive noise.

– A break is received.

When the framing error is detected:

Note: the extended prescaler is activated by set-

ting the SCIETPR or SCIERPR register to a value

other than zero. The baud rates are calculated as

follows:

Tx =

fCPU

Rx =

fCPU

16*ETPR*(PR*TR)

16*ERPR*(PR*RR)

– the FE bit is set by hardware

with:

– Data is transferred from the Shift register to the

SCIDR register.

) – No interrupt is generated. However this bit rises

t(s at the same time as the RDRF bit which itself

c generates an interrupt.

u The FE bit is reset by a SCISR register read oper-

d ation followed by a SCIDR register read operation.

ro 10.5.4.4 Conventional Baud Rate Generation

P The baud rate for the receiver and transmitter (Rx

te and Tx) are set independently and calculated as

le follows:

o fCPU

s Tx =

b (16*PR)*TR

fCPU

Rx =

(16*PR)*RR

- O with:

) PR = 1, 3, 4 or 13 (see SCP[1:0] bits)

t(s TR = 1, 2, 4, 8, 16, 32, 64,128

c (see SCT[2:0] bits)

du RR = 1, 2, 4, 8, 16, 32, 64,128

ro (see SCR[2:0] bits)

P All these bits are in the SCIBRR register.

te Example: If fCPU is 8 MHz (normal mode) and if

le PR = 13 and TR = RR = 1, the transmit and re-

ceive baud rates are 38400 baud.

so Note: The baud rate registers MUST NOT be

b changed while the transmitter or the receiver is en-

O abled.

ETPR = 1,..,255 (see SCIETPR register)

ERPR = 1,.. 255 (see SCIERPR register)

10.5.4.6 Receiver Muting and Wake-up Feature

In multiprocessor configurations it is often desira-

ble that only the intended message recipient

should actively receive the full message contents,

thus reducing redundant SCI service overhead for

all non addressed receivers.

The non addressed devices may be placed in

sleep mode by means of the muting function.

Setting the RWU bit by software puts the SCI in

sleep mode:

All the reception status bits can not be set.

All the receive interrupts are inhibited.

A muted receiver may be awakened by one of the

following two ways:

– by Idle Line detection if the WAKE bit is reset,

– by Address Mark detection if the WAKE bit is set.

Receiver wakes-up by Idle Line detection when

the Receive line has recognized an Idle Frame.

Then the RWU bit is reset by hardware but the

IDLE bit is not set.

Receiver wakes-up by Address Mark detection

when it received a “1” as the most significant bit of

a word, thus indicating that the message is an ad-

dress. The reception of this particular word wakes

up the receiver, resets the RWU bit and sets the

RDRF bit, which allows the receiver to receive this

10.5.4.5 Extended Baud Rate Generation

word normally and to use it as an address word.

The extended prescaler option gives a very fine

tuning on the baud rate, using a 255 value prescal-

er, whereas the conventional Baud Rate Genera-

tor retains industry standard software compatibili-

ty.

The extended baud rate generator block diagram

is described in the Figure 48

CAUTION: In Mute mode, do not write to the

SCICR2 register. If the SCI is in Mute mode during

the read operation (RWU = 1) and a address mark

wake up event occurs (RWU is reset) before the

write operation, the RWU bit is set again by this

write operation. Consequently the address byte is

lost and the SCI is not woken up from Mute mode.

The output clock rate sent to the transmitter or to

the receiver is the output from the 16 divider divid-

ed by a factor ranging from 1 to 255 set in the SCI-

ERPR or the SCIETPR register.

Doc ID 6996 Rev 5

73/139

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