HC705RC16GRSSLASHD datasheet(72/120 Pages) NXP

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Carrier Modulator Transmitter (CMT)

General Release Specification

MC68HC705RC16 — Rev. 3.0

Carrier Modulator Transmitter (CMT)

of the modulator. The secondary carrier high and low time values are

undefined out of reset. These bits must be written to non-zero values

before the carrier generator is enabled when operating in FSK mode.

IROLN and IROLP — IRO Latch Control

Reading IROLN or IROLP reads the state of the IRO latch. Writing

IROLN updates the IRO latch with the data being written on the

negative edge of the internal processor clock (fosc/2). Writing IROLP

updates the IRO latch on the positive edge of the internal processor

clock; for example, one fosc period later. The IRO latch is clear out of

reset.

NOTE:

Writing to CHR1 to update IROLN or to CLR1 to update IROLP will also

update the primary carrier high and low data values. Care should be

taken that bits 5–0 of the data to be written to CHR1 or CHL1 should

contain the desired values for the primary carrier high or low data.

9.5 Modulator

The modulator consists of a 12-bit down counter with underflow

detection which is loaded from the modulation mark period from the

mark buffer register, MBUFF. When this counter underflows, the

modulator gate is closed and a 12-bit comparator is enabled which

continually compares the logical complement of the contents of the (still)

decrementing counter with the contents of the modulation space period

is opened again. Should SREG = 0, the match will be immediate and no

space period will be generated (for instance, for FSK protocols which

require successive bursts of different frequencies). When the match

occurs, the counter is reloaded with the contents of MBUFF, SREG is

reloaded with the contents of its buffer, SBUFF, and the cycle repeats.

The MCGEN bit in the MCSR must be set to enable the modulator timer.

The 12-bit MBUFF and SBUFF registers are accessed through three

8-bit modulator period registers, MDR1, MDR2, and MDR3.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC705RC16GRS/D Datasheet(PDF) 72 Page - NXP Semiconductors