SDA5250 Datasheet, PDF (91/143 Pages) Siemens Semiconductor Group – TVTEXT 8-Bit Microcontroller

SDA 525x
The registers RELH and RELL (SFR-address E2_H and E1_H) are the reload registers,
CAPH and CAPL (SFR-addresses E4_H and E3_H) are the corresponding capture
registers. The reset value of these registers is undefined.
6.3.10 Serial Interface
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 described in this chapter depend on the internal system
clock, used by the serial interface. The internal system clock frequency of the serial
interface is defined by the oscillator frequency f_OSC and the setting of bit CDC in the
Advanced Function Register AFR of the special function registers (see
Chapter “Advanced Function Register” on page 115).
The serial port can operate in 4 modes:
Mode 0: Serial data enters and exits through RxD (P3.6). TxD (P3.7) 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
91
1998-04-08