P83C524 datasheet(30/76 Pages) PHILIPS

30 / 76 page

1997 Dec 15

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers

P83C524; P80C528; P83C528

12 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

SBUF SFR. Writing to SBUF loads the transmit register,

and reading SBUF accesses the physically separate

receive register. The Serial Port can operate in one of four

modes:

Mode 0 serial data enters and exits through RXD. TXD

outputs the shift clock. 8 bits are

transmitted/received: 8 data bits (LSB ﬁrst). The

baud rate is ﬁxed at 1/12 the oscillator frequency.

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

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

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

goes into RB8 in SCON SFR. The baud rate is

variable.

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

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

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

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

can be assigned the value of 0 or 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

SCON, while the stop bit is ignored. The baud

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

oscillator frequency.

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

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

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

(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 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.

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