P89C738 datasheet(26/64 Pages) PHILIPS

26 / 64 page

1998 Apr 07

Philips Semiconductors

Product speciﬁcation

8-bit Flash microcontrollers

P89C738; P89C739

12 FULL DUPLEX SERIAL PORT (UART)

The serial port is functionally similar to the implementation

in the 8052AH, with the possibility of two different baud

rates for receive and transmit with Timer 1 and Timer 2 as

baud rate generators. It is full duplex, meaning it can

receive and transmit simultaneously. It is also

receive-buffered, meaning it can commence reception of a

second byte before a previously received byte has been

read from the receive register. However, if the first byte still

has not been read by the time the reception of the second

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

Port receive and transmit registers are both accessed as

SFR SBUF. Writing to SBUF loads the transmit register,

and reading SBUF accesses the physically separate

receive register.

12.1

The Serial Port operating modes

The serial port can operate in one of 4 modes:

Mode 0 Serial data enters and exits through RXD.

TXD outputs the shift clock. Eight bits are

transmitted/received (LSB first). The baud rate is

fixed at 1

⁄12fclk.

Mode 1 10 bits are transmitted (through TXD) or received

(through RXD): a start bit (logic 0), 8 data bits

(LSB first), and a stop bit (logic 1). On receive,

the stop bit goes into RB8 in SFR SCON.

The baud rate is variable.

Mode 2 11 bits are transmitted (through TXD) or received

(through RXD): start bit (logic 0), 8 data bits (LSB

first), a programmable 9th data bit, and a stop bit

(logic 1). On transmit, the 9th data bit (TB8 in

SFR SCON) can be assigned the value of a

logic 0 or logic 1. For example, the parity bit (P in

the PSW) could be moved into TB8. On receive,

the 9th data bit goes into RB8 in SFR SCON,

while the stop bit is ignored. The baud rate is

programmable to either 1

⁄32 or 1⁄64fclk.

Mode 3 11 bits are transmitted (through TXD) or received

(through RXD): a start bit (logic 0), 8 data bits

(LSB first), a programmable 9th data bit and a

stop bit (logic 1). In fact, Mode 3 is the same as

Mode 2 in all respects except the baud rate.

The baud rate in Mode 3 is variable.

In all four modes, transmission is initiated by any

instruction that uses SFR SBUF as a destination register.

In Mode 0, reception is initiated by the condition RI = 0 and

REN = 1. Reception is initiated by incoming start bit if

REN = 1 in the other modes.

P89C738 Datasheet(PDF) 26 Page - NXP Semiconductors

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