MC68HC11KW1 Datasheet, PDF (129/238 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor HCMOS) microcontroller unit

7
SERIAL COMMUNICATIONS INTERFACE
The serial communications interface (SCI) is a universal asynchronous receiver transmitter
(UART). It has a non-return to zero (NRZ) format (one start, eight or nine data, and one stop bit)
that is compatible with standard RS-232 systems.
The SCI shares I/O with two of port D’s pins:
Pin
Alternative
function
PD0
RXD
7
PD1
TXD
The SCI transmit and receive functions are enabled by TE and RE respectively, in SCCR2.
The SCI features enabled on this MCU include: 13-bit modulus prescaler, idle line detect,
receiver-active flag, transmitter and receiver hardware parity. A block diagram of the enhanced
baud rate generator is shown in Figure 7-1. See Table 7-1 for example baud rate control values.
EXTAL
13-bit counter
Reset
13-bit compare ^EQ
SCBDH/L: SCI baud control
Internal
phase 2 clock
Sync
÷2
Transmitter
baud rate
clock
÷ 16
Receiver
baud rate
clock
Figure 7-1 SCI baud rate generator circuit diagram
MC68HC11KW1
SERIAL COMMUNICATIONS INTERFACE
7-1