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Doc. # 20480086.003

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Global Call Progress Tone Detector

4

MX613

Preliminary Information

Application Information ......

a. Set the

µP timer period to a period greater than the relevant frequency-band measurement period (13.16ms

or 39.47ms).

b. Each ‘Tone Measurement Complete’ interrupt from the MX613 must reset the

µP timer.

i. ‘Tone Measurement Complete' interrupt will not occur - the

µP timer will run.

ii. The

On-Chip Timer Operation

For frequency measurement, the MX613 counts the number of input cycles in a fixed time period. This fixed

period, measured by the continuous on-chip timer, is set to 13.16ms for HI Band inputs and 39.47ms for LO Band

inputs.

When the timer expires the following actions take place:

a. A HI or LO (“1” or “0”) band indication bit is latched into Bit-5 of the Serial Output Port.

b. The Frequency Counter count of 5-bits is latched into the Serial Output Port (Bit-4 [MSB] to Bit-0). The

Serial Output Port Contains 6-bits, if 8 Serial Clock edges are employed, two extra “0s”, which should be

ignored, will be output last.

c. An interrupt is generated (IRQ) to the

µProcessor. The contents of the Serial Output Port should be read

before the next interrupt is expected; if not data will be overwritten.

When the Chip Select input is set to “0” the interrupt is reset.

The On-Chip Timer and Frequency Counter will be reset in mid-count, and therefore unable to allow a valid

measurement, under the following conditions:

a. A change of decode frequency band.

b. Decoder disabled; signal input level out of specification or Level Detect input set to V

c. Signal Quality Assessment considered ‘Bad’.

d. Input signal frequency outside limits.

In Limits

Running

Enabled

Enabled

Out of Limits

Reset

Disabled

Disabled

(frozen to previous bit-5 level

V

DD

Running/Reset

Enabled/Disabled

Enabled

(dependent upon Quality measurement)

V

SS

Reset

Disabled

Disabled

(frozen to previous bit-5 level)

Level In

Timer

IRQ

Data Out

Frequency Band Discrimination

The input signal is amplified by a self-biased (zero-crossing) inverting amplifier and then ‘filtered’ to remove high-

frequency noise and jitter.

High (HI) and Low (LO) counters are employed to determine the input frequency band (HI = 900Hz to 2150Hz,

LO = 300Hz to 660Hz).

If the input frequency is in the LO Band, the device will operate as a LO Band decoder and will remain so until a

HI frequency signal is detected. If the input frequency is in the HI Band, the device will operate as a HI Band

decoder and will remain so until a LO frequency signal is detected.

Frequency band monitoring is continuous with the band selection taking place every 9.8ms. It will therefore take

9.8ms from Power-Up to set up the initial correct decode frequency band.

Principles of Decoder Operation

Level Detection

Because level and frequency discrimination operations take place in parallel, the audio signal should, under normal

circumstances, be input to both Signal In and Level In pins via coupling capacitors.

If the input signal level (Level In) is outside the preset ‘Must/Must Not Decode’ thresholds (see Specifications), the

Universal Call Progress Decoder will be disabled.

If it is wished to disregard signal input

levels at the Level In pin and attempt to decode under all conditions, the decoder

may be permanently enabled by holding the Level In pin at V

The MX613 can disabled by pulling Level In to V