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SA9401

5

Intrude Tone Generator

This module generates a square wave output based on the master clock of 2048kHz.

The Intrude Tone frequency is determined by the contents of the 16-bit Intrude Tone

Register (INTR_LO and INTR_HI) according to the formula:-

f

where n is the content of the INTR register.

The range of values in the register (from 0 to 65535) give Intrude tones in the range

15.625Hz to 1024kHz.

Cadence Timer

In any given Tone Plan the SA9401 assumes that any or all of the 9 (8 PCM tone

streams and one squarewave Intrude Tone) tones are required to have their own inde-

pendently defined cadence. A typical cadence is illustrated in FIGURE 1 above. Each

tone is assumed to comprise up to 4 cadence periods which repeat cyclically. The

duration of each period is controlled by the Cadence Timers which in turn comprise 10-

bit Counters. These timers are clocked by the five_ms_timebase generated by the

Clock Generator so that intervals of up to 5.12 seconds can be defined with a resolution

of 5ms. (10 bits => 1023: 1023*5ms = 5115ms)

The Cadence Controller controls the loading of the 10-bit counter and the sequencing

of the Cadence Position Counter. The duration of each period of the tone is denoted by

the parameter:-

CADm_n_LO = Period m, Tone stream n low-order 8 bits and

CADm_n_HI = Period m, Tone stream n high-order 2 bits

where 0

≤ m ≤ 3 and 0 ≤ n ≤ 8 (8 = Intrude Tone)

The Cadence Position Counter keeps track of the period being generated and during

period 0 the SA9401 generates a tone based on one Tone Block (A) while during the

period 2 (if used) the samples from another Block (B) are used. During periods 1 and 3

the silence sample is transmitted. This feature allows the sound of the tone to be

altered along with the cadence.

A continuous tone is created by loading values of 1(or any non-zero value),0,0,0 into

the registers CAD0_n to CAD3_n respectively. The zero value is interpreted by the

SA9401 as an instruction to ignore the period and to process the next one. With the

register contents shown the Cadence Controller continuously processes the first (ON)

period.

CADO_n

TONE_n_A

DR-01086

ON

OFF

CAD1_n

ON

CAD2_n

TONE_n_B

OFF

CAD3_n

FIGURE 1: TONE CADENCING