MC68HC datasheet(76/124 Pages) FREESCALE

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SERIAL COMMUNICATIONS INTERFACE

7-10

TECHNICAL DATA

Figure 7-3 SCI Baud Rate Diagram

7.7 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.

SCI BAUD GENERATOR

÷3

÷4

÷ 13

OSCILLATOR

AND

CLOCK GENERATOR

(÷ 4)

XTAL

EXTAL

INTERNAL BUS CLOCK (PH2)

1:1

SCP[1:0]

1:0

0:1

0:0

÷2

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

1:1:1

÷16

SCI

RECEIVE

BAUD RATE

(16X)

SCR[2:0]

SCI

TRANSMIT

BAUD RATE

(1X)

Freescale Semiconductor, Inc.

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