MC68HC11KA4TS Datasheet, PDF (37/68 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 the MC68HC11KA4/KA2. 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 the table of SCI baud
rate control values for standard values.
EXTAL
XTAL
OSCILLATOR
AND
CLOCK GENERATOR
(÷4)
E
AS
INTERNAL BUS CLOCK (PH2)
÷3
÷4
÷13
SCP[1:0]
0:0
0:1
1:0
1:1
SCR[2:0]
0:0:0
÷2
0:0:1
÷2
0:1:0
÷2
0:1:1
÷2
1:0:0
÷2
1:0:1
÷2
1:1:0
÷16
SCI
TRANSMIT
BAUD RATE
(1X)
÷2
1:1:1
SCI
RECEIVE
BAUD RATE
(16X)
Figure 9 SCI Baud Generator Circuit Diagram
SCI BAUD GENERATOR
MC68HC11KA4
MC68HC11KA4TS/D
MOTOROLA
37