68HC05CL48 datasheet(65/145 Pages) MOTOROLA

65 / 145 page

June 11, 1997

GENERAL RELEASE SPECIFICATION

MC68HC05CL48

TIMER

MOTOROLA

REV 2.0

8-13

IC1F - Input Capture Flag

1 =

Flag set when a selected polarity edge has been sensed by the

input capture edge detector.

0 =

Flag cleared by reading the timer status register (with IC1F set)

followed by accessing the low byte ($14) of the input capture

IC2F - Input Capture Flag

1 =

Flag set when a selected polarity edge has been sensed by the

input capture edge detector.

0 =

Flag cleared by reading the timer status register (with IC2F set)

followed by accessing the low byte ($10) of the input capture

OC1F - Output Compare 1 Flag

1 =

Flag set when the output compare register 1 contents matches the

contents of the free running counter.

0 =

Flag cleared by reading the timer status register (with OC1F set)

and then accessing the low byte ($16) of the output compare 1

OC2F - Output Compare 2 Flag

1 =

Flag set when the output compare register 2 contents matches the

contents of the free running counter.

0 =

Flag cleared by reading the timer status register (with OC2F set)

and then accessing the low byte ($18) of the output compare 1

TOF - Timer OVerﬂow Flag

1 =

Flag set by transition of the free running counter from $FFFF to

$0000.

0 =

Flag cleared by reading the timer status register (with TOF set)

followed by an access of the free running counter least signiﬁcant

byte ($1A).

Accessing the timer status register satisﬁes the ﬁrst condition required to clear

status bits. The remaining step is to access the register corresponding to the

status bit.

A problem can occur when using the timer overﬂow function and reading the free-

running counter at random times to measure an elapsed time. Without

incorporating the proper precautions into software, the timer overﬂow ﬂag could

unintentionally be cleared if:

The timer status register is read or written when TOF is set, and

The LSB of the free-running counter is read but not for the purpose of

servicing the ﬂag.

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