SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 51

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

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.
In all four modes, transmission is initiated by any instruction that uses S0BUF as a destination
register. Reception is initiated in mode 0 by the condition RI0 = 0 and REN0 = 1. Reception is
initiated in the other modes by the incoming start bit if REN0 = 1. The serial interfaces also provide
interrupt requests when a transmission or a reception of a frame has completed. The corresponding
interrupt request flags for serial interface 0 are TI0 or RI0, resp. See section 8 for more details about
the interrupt structure. The interrupt request flags TI0 and RI0 can also be used for polling the serial
interface 0 if the serial interrupt is not to be used (i.e. serial interrupt 0 not enabled).
The control and status bits of the serial channel 0 in special function register S0CON are illustrated
in figure 7-8. Figure 7-7 shows the special function register S0BUF which is the data register for
receive and transmit. The following table summarizes the operating modes of serial interface 0.
Serial Interface 0, Mode Selection
SM0
0
0
1
1
Figure 7-7
Special Function Register S0BUF (Address 99 H )
Receive and transmit buffer of serial interface 0. Writing to S0BUF loads the transmit register and
initiates transmission. Reading out S0BUF accesses a physically separate receive register.
Semiconductor Group
99 H
SM1
0
1
0
1
Serial interface 0 buffer register
Mode
0
1
2
3
52
Shift register
8-bit UART
9-bit UART
Descriptions
9-bit UART
On-Chip Peripheral Components
f
Variable
f
Variable
Baud Rate
OSC
OSC
/12
/64 or
S0BUF
f
OSC
/32