SDA55XX Datasheet, PDF (117/230 Pages) Infineon Technologies AG – Preliminary & Confidential

SDA 55xx
Preliminary & Confidential
UART
11
UART
The serial port is full duplex, meaning it can transmit and receive 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 hasn’t been read by the time reception of the second byte is complete, one of
the bytes will be lost). The serial port receive and transmit registers are both accessed
at special function register SBUF. Writing to SBUF loads the transmit register, and
reading SBUF accesses a physically separate receive register.
The frequencies and baud rates depend on the internal system clock, used by the serial
interface.
The serial port can operate in 4 modes:
11.1
Modes
Mode 0:Serial data enters and exits through RxD (P3.7). TxD (P3.1) outputs the shift
clock.
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 reception, the stop bit goes into RB8 in
special function register SCON. 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 transmission,
the 9th data bit (TB8 in SCON) can be assigned the value of 0 or 1. Or, for example, the
parity bit (P, in the PSW) could be moved into TB8. On reception, the 9th data bit goes
into RB8 in the special function register SCON, while the stop bit is ignored. The baud
rate is programmable via SFR-Bit SMOD.
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.
Semiconductor Group
117
User’s Manual July 99