UPSD3313D-40U6T datasheet(81/231 Pages) STMICROELECTRONICS

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uPSD33xx

SERIAL UART INTERFACES

uPSD33xx devices provide two standard 8032

UART serial ports.

–

The first port, UART0, is connected to pins

RxD0 (P3.0) and TxD0 (P3.1)

–

The second port, UART1 is connected to pins

RxD1 (P1.2) and TxD1 (P1.3). UART1 can

optionally be routed to pins P4.2 and P4.3 as

described in Alternate Functions, page 59.

The operation of the two serial ports are the same

and are controlled by two SFRs:

■

SCON0 (Table 45., page 82) for UART0

■

SCON1 (Table 46., page 83) for UART1

Each UART has its own data buffer accessed

through an SFR listed below:

■

SBUF0 for UART0, address 99h

■

SBUF1 for UART1, address D9h

When writing SBU0 or SBUF1, the data automati-

cally loads into the associated UART transmit data

a different physical register, which is the receive

Note: For simplicity in the remaining UART dis-

cussions, the suffix “0” or “1” will be dropped when

referring to SFR registers and bits related to

UART0 or UART1, since each UART interface has

identical operation. Example, SBUF0 and SBUF1

will be referred to as just SBUF.

Each UART serial port can be full-duplex, meaning

it can transmit and receive simultaneously. Each

UART is also receive-buffered, meaning it can

commence reception of a second byte before a

previously received byte has been read from the

SBUF Register. However, if the first byte still has

not been read by the time reception of the second

byte is complete, one of the bytes will be lost.

UART Operation Modes

Each UART can operate in one of four modes, one

mode is synchronous, and the others are asyn-

chronous as shown in Table 44.

Mode 0. Mode 0 provides asynchronous, half-du-

plex operation. Serial data is both transmitted, and

received on the RxD pin. The TxD pin outputs a

shift clock for both transmit and receive directions,

thus the MCU must be the master. Eight bits are

transmitted/received LSB first. The baud rate is

fixed at 1/12 of fOSC.

Mode 1. Mode 1 provides standard asynchro-

nous, full-duplex communication using a total of 10

bits per data byte. Data is transmitted through TxD

and received through RxD with: a Start Bit (logic

'0'), eight data bits (LSB first), and a Stop Bit (logic

'1'). Upon receive, the eight data bits go into the

SFR SBUF, and the Stop Bit goes into bit RB8 of

the SFR SCON. The baud rate is variable and de-

rived from overflows of Timer 1 or Timer 2.

Mode 2. Mode 2 provides asynchronous, full-du-

plex communication using a total of 11 bits per

data byte. Data is transmitted through TxD and re-

ceived through RxD with: a Start Bit (logic '0');

eight data bits (LSB first); a programmable 9th

data bit; and a Stop Bit (logic '1'). Upon Transmit,

the 9th data bit (from bit TB8 in SCON) can be as-

signed the value of '0' or '1.' Or, for example, the

Parity Bit (P, in the PSW) could be moved into

TB8. Upon receive, the 9th data bit goes into RB8

in SCON, while the Stop Bit is ignored. The baud

rate is programmable to either 1/32 or 1/64 of

fOSC.

Mode 3. Mode 3 is the same as Mode 2 in all re-

spects except the baud rate is variable like it is in

Mode 1.

In all four modes, transmission is initiated by any

instruction that uses SBUF as a destination regis-

ter. Reception is initiated in Mode 0 by the condi-

tion RI = 0 and REN = 1. Reception is initiated in

the other modes by the incoming Start Bit if

REN = 1.

Table 44. UART Operating Modes

Mode

Synchronization

Bits of SFR,

SCON

Baud Clock

Data

Bits

Start/Stop Bits

See Figure

SM0

SM1

Synchronous

fOSC/12

None

Figure

28., page 86

Asynchronous

Timer 1 or Timer 2 Overflow

1 Start, 1 Stop

Figure

30., page 88

Asynchronous

fOSC/32 or fOSC/64

1 Start, 1 Stop

Figure

32., page 90

Asynchronous

Timer 1 or Timer 2 Overflow

1 Start, 1 Stop

Figure

34., page 91

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