SA9401
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
int
= 2048kHz/(2*(n+1))
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)
ON
OFF
ON
OFF
TONE_n_A
CADO_n
DR-01086
CAD1_n
TONE_n_B
CAD2_n
CAD3_n
FIGURE 1: TONE CADENCING
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.
5
sames
SAMES [ SAMES ]
