M68HC11E Datasheet, PDF (129/268 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
Status Flags and Interrupts
EXTAL
XTAL
OSCILLATOR
AND
CLOCK GENERATOR
(÷4)
E
AS
INTERNAL BUS CLOCK (PH2)
÷3
0:0:0
0:0:1
÷4
÷ 13
÷ 39
SCP[2:0]*
0:1:0
0:1:1
1:0:0
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)
*SCP2 is present only on MC68HC(7)11E20.
Figure 7-9. MC68HC(7)11E20 SCI Baud Rate
Generator Block Diagram
7.8 Status Flags and Interrupts
The SCI transmitter has two status flags. These status flags can be read by
software (polled) to tell when the corresponding condition exists. Alternatively, a
local interrupt enable bit can be set to enable each of these status conditions to
generate interrupt requests when the corresponding condition is present. Status
flags are automatically set by hardware logic conditions, but must be cleared by
software, which provides an interlock mechanism that enables logic to know when
software has noticed the status indication. The software clearing sequence for
M68HC11E Family — Rev. 5
MOTOROLA
Serial Communications Interface (SCI)
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Data Sheet
129