MC68711E20CFNE3 Datasheet, PDF (116/242 Pages) –

Serial Communications Interface (SCI)
EXTAL
XTAL
OSCILLATOR
AND
CLOCK GENERATOR
(÷4)
E
AS
INTERNAL BUS CLOCK (PH2)
÷3
0:0:0
0:0:1
÷4
0:1:0
÷ 13
÷ 39
SCP[2:0]*
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 these flags is automatic. Functions that are normally
performed in response to the status flags also satisfy the conditions of the clearing sequence.
M68HC11E Family Data Sheet, Rev. 5.1
116
Freescale Semiconductor