SAB80515 Datasheet, PDF (47/270 Pages) Siemens Semiconductor Group – 8-Bit Single-Chip Microcontroller Family

On-Chip Peripheral Components
7.2 Serial Interfaces
The serial port of the SAB 80(C)515S enables communication between microcontrollers or between
the microcontroller and peripheral devices.
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 has not been read by the time
reception of the second byte is complete, the last received byte will be lost). The serial channel is
completely compatible with the serial channel of the SAB 80(C)51.
7.2.1 Operating Modes of Serial Interface
The serial interface can operate in four modes (one synchronous mode, three asynchronous
modes). The baud rate clock for this interface is derived from the oscillator frequency (mode 0, 2)
or generated either by timer 1 or by a dedicated baud rate generator (mode 1, 3). A more detailed
description of how to set the baud rate will follow in section 7.2.3.
Mode 0: shift register (synchronous) mode:
Serial data enters and exits through RxD. TxD outputs the shift clock. 8 data bits are transmitted/
received (LSB first). The baud rate is fixed at 1/12 of the oscillator frequency.
Mode 1: 8-bit UART, variable baud rate:
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: 9-bit UART, fixed baud rate:
11 bits are transmitted (through TxD) or received (through RxD): a start bit (0), 8 data bits (LSB first),
a programmable 9th bit, and a stop bit (1). On transmission, the 9th data bit (TB8 in SCON) can be
assigned to the value of 0 or 1. For example, the parity bit (P in the PSW) could be moved into TB8
or a second stop bit by setting TB8 to 1. On reception the 9th data bit goes into RB8 in special
function register SCON, while the stop bit is ignored. The baud rate is programmable to either 1/32
or 1/64 of the oscillator frequency.
Mode 3: 9-bit UART, variable baud rate:
11 bits are transmitted (through TxD) or received (through RxD): a start bit (0), 8 data bits (LSB first),
a programmable 9th bit, and a stop bit (1). On transmission, the 9th data bit (TB8 in SCON) can be
assigned to the value of 0 or 1. For example, the parity bit (P in the PSW) could be moved into TB8
or a second stop bit by setting TB8 to 1. On reception, the 9th data bit goes into RB8 in special
function register SCON, while the stop bit is ignored. 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
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