MC68HC711K4CFN4 Datasheet, PDF (49/80 Pages) Motorola, Inc – 8-Bit Microcontroller

7 Serial Communications Interface
The SCI, a universal asynchronous receiver transmitter (UART) serial communications interface, is one
of two independent serial I/O subsystems in M68HC11 K-series MCUs. Rearranging registers and con-
trol bits used in previous M68HC11 family devices has enhanced the existing SCI system and added
new features, which include the following:
• A 13-bit modulus prescaler that allows greater baud rate control
• A new idle mode detect, independent of preceding serial data
• A receiver active flag
• Hardware parity for both transmitter and receiver
The enhanced baud rate generator is shown in the following diagram. Refer to Table 7 for standard val-
ues.
EXTAL
13-BIT COUNTER
RESET
INTERNAL
PHASE 2 CLOCK
13-BIT COMPARE
=
SCBDH/L SCI BAUD CONTROL
SYNCH
÷2
÷ 16
Figure 9 SCI Baud Generator Circuit Diagram
RECEIVER
BAUD RATE
CLOCK
TRANSMITTER
BAUD RATE
CLOCK
M68HC11 K Series
MC68HC11KTS/D
MOTOROLA
49