MC9S08RC8 Datasheet, PDF(116/234 Page) Freescale Semiconductor, Inc – Microcontrollers

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MC9S08RC8 Datasheet, PDF (116/234 Pages) Freescale Semiconductor, Inc – Microcontrollers

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Carrier Modulator Transmitter (CMT) Block Description

texspace = tspace + (tmark + tspace) x (number of modulation periods)

For an example of extended space operation, see Figure 8-7.

NOTE

The EXSPC feature can be used to emulate a zero mark event.

SET EXSPC

CLEAR EXSPC

Eqn. 8-9

Figure 8-7. Extended Space Operation

8.5.3.2 EXSPC Operation in FSK Mode

In FSK mode, the modulator continues to count carrier out clocks, alternating between the primary and

secondary registers at the end of each modulation period.

To calculate the length of an extended space in FSK mode, the user must know whether the EXSPC bit

was set on a primary or secondary modulation period, as well as the total number of both primary and

secondary modulation periods completed while the EXSPC bit is high. A status bit for the current

modulation is not accessible to the CPU. If necessary, software should maintain tracking of the current

modulation cycle (primary or secondary). The extended space period ends at the completion of the space

period time of the modulation period during which the EXSPC bit is cleared.

If the EXSPC bit was set during a primary modulation cycle, use the equation:

texspace = (tspace)p + (tmark + tspace)s + (tmark + tspace)p +...

Eqn. 8-10

Where the subscripts p and s refer to mark and space times for the primary and secondary modulation

cycles.

If the EXSPC bit was set during a secondary modulation cycle, use the equation:

texspace = (tspace)s + (tmark + tspace)p + (tmark + tspace)s +...

Eqn. 8-11

8.5.4 Transmitter

The transmitter output block controls the state of the infrared out pin (IRO). The modulator output is gated

on to the IRO pin when the modulator/carrier generator is enabled. When the modulator/carrier generator

is disabled, the IRO pin is controlled by the state of the IRO latch.

A polarity bit in the CMTOC register enables the IRO pin to be high true or low true.

MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11

116

Freescale Semiconductor

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