Siemens SAB 80515 Series, User Manual, Page: 54 / 270

Semiconductor Group 54
On-Chip Peripheral Components
Table 7-5
Baud Rates of Serial Interface 0
7.2.4 Detailed Description of the Operating Modes
The following sections give a more detailed description of the several operating modes of the serial
interface.
7.2.4.1 Mode 0, Synchronous Mode
Serial data enters and exits through RxD. TxD outputs the shift clock. 8 bits are transmitted/
received: 8 data bits (LSB first). The baud rate is fixed at 1/12 of the oscillator frequency.
Figures 7-16 a) and b) show a simplified functional diagram of the serial port in mode 0, and
associated timing.
Transmission is initiated by any instruction that uses SBUF as a destination register. The "write-to-
SBUF" signal at S6P2 also loads a 1 into the 9th bit position of the transmit shift register and tells
the TX control block to commence a transmission. The internal timing is such that one full machine
cycle will elapse between "write-to-SBUF" and activation of SEND.
Baud Rate Derived
from Interface
Mode Baud Rate
Timer 1 in mode 1 1, 3
Timer 1 in mode 2 1, 3
Oscillator 2
Baud rate generator 1, 3
x (timer 1 overflow rate)
2 SMOD 1
16
x
2
2 SMOD 1
16
x
2
x
f
OSC
12 x (256 – (TH1))
2
SMOD
1
16
x
2
x
f
OSC
2
2 SMOD 1
16
x
2
x
f
OSC
1250
*