MC68HC11EA9 Datasheet, PDF (47/58 Pages) Motorola, Inc – 8 BIT HCMOS SINGLE CHIP MICROCONTOROLLER WITH A/D CONVERTER

Freescale Semiconductor, Inc.
8 Serial Communications Interface
The SCI, a universal asynchronous receiver transmitter (UART) serial communications interface, is an
independent serial I/O subsystem in MC68HC(7)11EA9 MCUs. The registers and control bits used in
previous M68HC11 SCI systems have been rearranged and new features added. New or enhanced fea-
tures 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.
SCI BAUD CLOCK
EXTAL ÷ 2, IF MCS = 0
4XCLK ÷ 2, IF MCS = 1
13-BIT COUNTER
RESET
13-BIT COMPARE =
SCBDH/L SCI BAUD CONTROL
INTERNAL
PHASE 2 CLOCK
(PH2)
SYNCHRONIZE
÷2
WITH PH2
÷ 16
Figure 11 SCI Baud Generator Circuit Diagram
RECEIVER
BAUD RATE
CLOCK
TRANSMITTER
BAUD RATE
CLOCK
EA9 BAUD GEN BLOCK
MC68HC11EA9
MC68HC11EA9TS/D
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