V23 / Bell 202 Modem

CMX624

 2003 CML Microsystems Plc

10

D/624/7

-70

-60

-50

-40

-30

-20

-10

0

10

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10000

100000

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dBm

V23

Bell 202

Figure 5 Maximum Out of Band Tx Line Energy Limits

1.5.8

Transmit Output Buffer

This buffer amplifier, connected to the TXN, TXO and TXON pins, is intended for use as a Tx line driver as

shown in Section 1.6.1. Two symmetrical outputs are provided for use with a balanced load to give

If the buffer is used as a balanced line driver, then bit 6 of the SETUP Register should be set to ‘1’ (TXON

output enabled). Setting bit 6 to ‘0’ disables the TXON output and the buffer draws less current from the

supply. When bit 6 is set to '0' the TXON pin should be left open circuit. N.B. The TXO output is unaffected

by this bit.

1.5.9

Ring Signal Detector

This block, which functions even in Zero Power mode, can be used to detect a telephone line Ring Signal

or Line Voltage Reversal and then generate a Interrupt Request signal to wake up the µC at the start of a

call. Suitable interface circuits are shown in Section 1.6.2.

The output of this block is the ‘Ring Detect’ line shown in Figure 1 which directly drives bit 6 of the FLAGS

Register. Any ‘0’ to ‘1’ or ‘1’ to ‘0’ change on this line will also set the ‘Ring Detect Change’ bit (5) of the

FLAGS Register.

Change’ bit (5) of the IRQ MASK Register set to ‘0’.