TCM3105DWL, TCM3105JE, TCM3105JL

TCM3105NE, TCM3105NL

FSK MODEM

SCTS019C – NOVEMBER 1985 – REVISED MAY 1994

7

POST OFFICE BOX 655303

POST OFFICE BOX 1443

carrier detect

The carrier-detect circuits comprise an energy detector and digital delay. The energy detector compares the

total signal level at the output of the receive filter to an externally set threshold level on the CDL input. The

comparator has a 2.5-dB hysteresis and a delay to allow for momentary signal loss and to prevent oscillation.

The output detector is available on CDT where a high level indicates that a carrier is present. The data output

is clamped to a mark condition when the carrier-detect output switches off at the end of transmission.

control and timing

An on-chip oscillator runs from an external 4.4336-MHz crystal connected between OSC1 and OSC2 or an

external signal driving OSC1. A clock signal equal to 16 times the highest selected bit rate (transmit or receive)

is available on the CLK output.

The single-supply rail means that all analog functions are referenced to an internally generated reference. All

analog inputs and outputs must be ac coupled.

transmit and receive modes

The various modes of operation of the TCM3105 are given in Table 1. The data convention is that a logic high

is a mark and a logic low is a space.