68HC05CL48 datasheet(86/145 Pages) MOTOROLA

86 / 145 page

GENERAL RELEASE SPECIFICATION

June 11, 1997

MOTOROLA

CALLER-ID

MC68HC05CL48

11-2

REV 2.0

11.1

FSK DEMODULATOR

The recovered signal consists of both the channel seizure information and the

message words. The original serial raw data is made available via the MCU

registers. See Section 11.7.2.

11.2

CARRIER DETECTOR

The Carrier Detect block will validate the carrier signal from the ﬁlter section. The

asynchronous carrier signal is considered valid if present for a minimum of 25ms.

A carrier dropout is conﬁrmed if it is silent for more than 8ms. The carrier detect

signal will remain low until a dropout condition is detected. The carrier detect

output is available in a read-only register (CD) in Control/Status Register 2

(CLCSR2). It can also be overwritten by writing to CDO (Carrier Detect Override)

in the Control/Status Register 1 (CLCSR1) when enabled by writing a ‘1’ to CDOE

(Carrier Detect Override Enable) in the CLCSR3 register. A valid carrier can also

produce an interrupt to the CPU when enabled by the CDIE bit in CLCSR1. See

Section 11.7.1 and Section 11.7.2

Figure 11-2. Carrier Detect Interface

11.3

RT_L INTERRUPT

Figure 11-3 shows that the RT_L pin connected to a ring time circuit. When RDI1

is ‘low’, RT_L is pulled high by the external pull-up resistor. When RDI1 rises

above 1.0 volt, RT_L will be pulled low by the open-drain NMOS transistor and an

interrupt will be generated.

Note: RT_L interrupt is permanently disabled in the current design and can only

be enabled by a Metal Mask Option.

Carrier Detect

CDO

CDOE

CDIE

CDIF

Read

Interrupt

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