C509-L_97 Datasheet, PDF (160/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
6.5
Serial Interfaces
The C509-L has two serial interfaces which are functionally nearly identical concerning the
asynchronous modes of operation. The two channels are full-duplex, meaning they can transmit
and receive simultaneously. They are also receive buffered, meaning they 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 0 is completely compatible with the
serial channel of the C501. Serial channel 1 has the same functionality in its asynchronous modes,
but the synchronous mode is missing.
6.5.1 Serial Interface 0
6.5.1.1 Operating Modes of Serial Interface 0
The serial interface 0 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 6.5.1.3.
Mode 0: Shift register (synchronous) mode:
Serial data enters and exits through RXD0. TXD0 outputs the shift clock. 8 data bits are
transmitted/received (LSB first). The baud rate is fixed at 1/6 of the oscillator frequency.
Mode 1: 8-bit UART, variable baud rate:
10 bits are transmitted (through TXD0) or received (through RXD0): a start bit (0), 8 data bits (LSB
first), and a stop bit (1). On reception, the stop bit goes into RB80 in special function register
S0CON. The baud rate is variable.
Mode 2: 9-bit UART, fixed baud rate:
11 bits are transmitted (through TXD0) or received (through RXD0): a start bit (0), 8 data bits (LSB
first), a programmable 9th bit, and a stop bit (1). On transmission, the 9th data bit (TB80 in S0CON)
can be assigned to the value of 0 or 1. For example, the parity bit (P in the PSW) could be moved
into TB80 or a second stop bit by setting TB80 to 1. On reception the 9th data bit goes into RB80
in special function register S0CON, while the stop bit is ignored. The baud rate is programmable to
either 1/16 or 1/32 of the oscillator frequency.
Mode 3: 9-bit UART, variable baud rate:
11 bits are transmitted (through TXD0) or received (through RXD0): a start bit (0), 8 data bits (LSB
first), a programmable 9th bit, and a stop bit (1). On transmission, the 9th data bit (TB80 in S0CON)
can be assigned to the value of 0 or 1. For example, the parity bit (P in the PSW) could be moved
into TB80 or a second stop bit by setting TB80 to 1. On reception, the 9th data bit goes into RB80
in special function register S0CON, 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
6-82
1997-10-01