Motorola MC68HC05RC8 User Manual

General Release Specification

MC68HC05RC16 — Rev. 3.0

78

Carrier Modulator Transmitter (CMT)

MOTOROLA

The mark and space time equations for FSK mode are:

Where f

cg

 is the frequency output from the carrier generator, setting the

DIV2 bit in the MCSR will double mark and space times.

In either time or FSK mode, the space period can be made longer than
the maximum possible value of SBUFF. Setting the EXSPC bit in the
MCSR will force the modulator to treat the next modulation period
(beginning with the next load of MBUFF/SBUFF) as a space period
equal in length to the mark and space counts combined. Subsequent
modulation periods will consist entirely of these extended space periods
with no mark periods. Clearing EXSPC will return the modulator to
standard operation at the beginning of the next modulation period. To
calculate the length of an extended space in time mode, use the
equation:

Where:

the subscripts 1, 2, ... n refer to the modulation periods that elapsed
while the EXSPC bit was set.

Similarly, to calculate the length of an extended space in FSK mode, use
the equation:

t

mark

MBUFF

1

+

f

cg

-------------------------------

s

sec

=

t

space

SBUFF

f

cg

---------------------

s

sec

=

((SBUFF

1

)+(MBUFF

2

+1+SBUFF

2

) +... (MBUFF

n

+1+SBUFF

n

)) x 8

f

osc

t

exspace

 =

secs

((SBUFF

1

)+(MBUFF

2

+1+SBUFF

2

)+... (MBUFF

n

+1+SBUFF

n

))

f

cg

t

exspace

 =

secs