Datasheet

C505/C505C/C505A/C505CA
Data Sheet 33 12.00
Serial Interface (USART)
The serial port is full duplex and can operate in four modes (one synchronous mode, three
asynchronous modes) as illustrated in Table 7.
For clarification some terms regarding the difference between "baud rate clock" and "baud rate"
should be mentioned. In the asynchronous modes
the serial interfaces require a clock rate which is
16 times the baud rate for internal synchronization. Therefore, the baud rate generators/timers have
to provide a "baud rate clock" (output signal in Figure 14 to the serial interface which - there divided
by 16 - results in the actual "baud rate". Further, the abbrevation f
OSC
refers to the oscillator
frequency (crystal or external clock operation).
The variable baud rates for modes 1 and 3 of the serial interface can be derived either from timer 1
or from a decdicated baud rate generator (see Figure 14).
Table 7
USART Operating Modes
Mode
SCON Description
SM0 SM1
0 0 0 Shift register mode, fixed baud rate
Serial data enters and exits through R×D; T×D outputs the shift
clock; 8-bit are transmitted/received (LSB first)
1 0 1 8-bit UART, variable baud rate
10 bits are transmitted (through T×D) or received (at R×D)
2 1 0 9-bit UART, fixed baud rate
11 bits are transmitted (through T×D) or received (at R×D)
3 1 1 9-bit UART, variable baud rate
Like mode 2