MC68HC908AZ32ACFU MOTOROLA [Motorola, Inc], MC68HC908AZ32ACFU Datasheet - Page 240

• Manufacturer Part Number: MC68HC908AZ32ACFU
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Serial Communications Interface (SCI)
Advance Information
240
Software latency may allow an overrun to occur between reads of SCS1
and SCDR in the flag-clearing sequence.
flag-clearing sequence and an example of an overrun caused by a
delayed flag-clearing sequence. The delayed read of SCDR does not
clear the OR bit because OR was not set when SCS1 was read. Byte 2
caused the overrun and is lost. The next flag-clearing sequence reads
byte 3 in the SCDR instead of byte 2.
In applications that are subject to software latency or in which it is
important to know which byte is lost due to an overrun, the flag-clearing
routine can check the OR bit in a second read of SCS1 after reading the
data register.
Freescale Semiconductor, Inc.
bit in SCC3 is also set. The data in the shift register is lost, but the data
already in the SCDR is not affected. Clear the OR bit by reading SCS1
with OR set and then reading the SCDR. Reset clears the OR bit.
For More Information On This Product,
1 = Receive shift register full and SCRF = 1
0 = No receiver overrun
BYTE 1
BYTE 1
Serial Communications Interface (SCI)
Go to: www.freescale.com
READ SCDR
READ SCS1
Figure 16-15. Flag Clearing Sequence
SCRF = 1
BYTE 1
OR = 0
READ SCDR
READ SCS1
DELAYED FLAG CLEARING SEQUENCE
NORMAL FLAG CLEARING SEQUENCE
BYTE 2
BYTE 2
SCRF = 1
BYTE 1
OR = 0
READ SCDR
READ SCS1
SCRF = 1
BYTE 2
OR = 0
Figure 16-15
BYTE 3
BYTE 3
68HC908AZ32A — Rev 0.0
READ SCDR
READ SCDR
READ SCS1
READ SCS1
SCRF = 1
SCRF = 1
BYTE 3
BYTE 3
OR = 1
OR = 0
shows the normal
BYTE 4
BYTE 4
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