ST92F124 datasheet(218/429 Pages) STMICROELECTRONICS

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MULTIPROTOCOL SERIAL COMMUNICATIONS INTERFACE (SCI-M)

MULTIPROTOCOL SERIAL COMMUNICATIONS INTERFACE (Cont’d)

10.5.5.1 Data transfer

Data to be transmitted by the SCI is first loaded by

the program into the Transmitter Buffer Register.

The SCI will transfer the data into the Transmitter

Shift Register when the Shift Register becomes

available (empty). The Transmitter Shift Register

converts the parallel data into serial format for

transmission via the SCI Alternate Function out-

put, Serial Data Out. On completion of the transfer,

the transmitter buffer register interrupt pending bit

will be updated. If the selected word length is less

than 8 bits, the unused most significant bits do not

need to be defined.

Incoming serial data from the Serial Data Input pin

is converted into parallel format by the Receiver

Shift Register. At the end of the input data frame,

the valid data portion of the received word is trans-

ferred from the Receiver Shift Register into the Re-

ceiver Buffer Register. All Receiver interrupt con-

ditions are updated at the time of transfer. If the

selected character format is less than 8 bits, the

unused most significant bits will be set.

The Frame Control and Status block creates and

checks the character configuration (Data length

and number of Stop bits), as well as the source of

the transmitter/receiver clock.

The internal Baud Rate Generator contains a pro-

grammable divide by “N” counter which can be

used to generate the clocks for the transmitter

and/or receiver. The baud rate generator can use

INTCLK or the Receiver clock input via RXCLK.

The Address bit/D9 is optional and may be added

to any word in Asynchronous and Serial Expan-

sion modes. It is commonly used in network or ma-

chine control applications. When enabled (AB set),

an address or ninth data bit can be added to a

transmitted word by setting the Set Address bit

(SA). This is then appended to the next word en-

tered into the (empty) Transmitter Buffer Register

and then cleared by hardware. On character input,

a set Address Bit can indicate that the data pre-

ceding the bit is an address which may be com-

pared in hardware with the value in the Address

Compare Register (ACR) to generate an Address

Match interrupt when equal.

The Address bit and Address Comparison Regis-

ter can also be combined to generate four different

types of Address Interrupt to suit different proto-

cols, based on the status of the Address Mode En-

able bit (AMEN) and the Address Mode bit (AM) in

the CHCR register.

The character match Address Interrupt mode may

be used as a powerful character search mode,

generating an interrupt on reception of a predeter-

mined character e.g. Carriage Return or End of

Block codes (Character Match Interrupt). This is

the only Address Interrupt Mode available in Syn-

chronous mode.

The Line Break condition is fully supported for both

transmission and reception. Line Break is sent by

setting the SB bit (IDPR). This causes the trans-

mitter output to be held low (after all buffered data

has been transmitted) for a minimum of one com-

plete word length and until the SB bit is Reset.

Break cannot be inserted into the transmitted

frame for the Synchronous mode.

Testing of the communications channel may be

performed using the built-in facilities of the SCI pe-

ripheral. Auto-Echo mode and Loop-Back mode

may be used individually or together. In Asynchro-

nous, Asynchronous with Synchronous Clock and

Serial Expansion modes they are available only on

SIN/SOUT pins through the programming of AEN/

LBEN bits in CCR. In Synchronous mode (SMEN

set) the above configurations are available on SIN/

SOUT, RXCLK/CLKOUT and DCD/RTS pins by

programming the AEN/LBEN bits and independ-

ently of the programmed polarity. In the Synchro-

nous mode case, when AEN is set, the transmitter

outputs (data, clock and control) are disconnected

from the I/O pins, which are driven directly by the

receiver input pins (Auto-Echo mode: SOUT=SIN,

CLKOUT=RXCLK and RTS=DCD, even if they act

on the internal receiver with the programmed po-

larity/edge). When LBEN is set, the receiver inputs

(data, clock and controls) are disconnected and

the transmitter outputs are looped-back into the re-

ceiver section (Loop-Back mode: SIN=SOUT, RX-

CLK=CLKOUT, DCD=RTS. The output pins are

locked to their programmed stand-by level and the

status of the INPL, XCKPL, DCDPL, OUTPL,

OCKPL and RTSPL bits in the SICR register are ir-

relevant). Refer to Figure 111, Figure 112, and

Figure 113 for these different configurations.

Table 44. Address Interrupt Modes

(1) Not available in Synchronous mode

If 9th Data Bit is set (1)

If Character Match

If Character Match and 9th Data Bit is set(1)

If Character Match Immediately Follows BREAK (1)

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