2001 May 07
9
Philips Semiconductors
Preliminary specification
Digital Signal Processor
SAA7715H
8
FUNCTIONAL DESCRIPTION
8.1
PLL division factors for different clock inputs
An on-chip PLL generates the clock for the DSP. The DSP runs at a selectable frequency of maximum 70 MHz. The clock
is generated with the PLL that uses the CLK_IN of the chip to generate the DSP clock. Table 2 gives the division factors
and the values of the DSP_TURBO and the DIV_CLK_IN bits that need to be set via I
2
C-bus (see Table 10).
Table 2
PLL division factor per clock input.
The above table does NOT imply that the clock input is restricted to the values given in this table. The clock input is
restricted to be within the range of 8.192 to 12.228 MHz. For higher clock frequencies pin DIV_CLK_IN should be set to
logic 1 performing a divide by 2 of the CLK_IN signal and thereby doubling the CLK_IN frequency range that is allowed
(16.384 to 24.576 MHz).
8.2
The word select PLL
A second on-chip PLL generates a selectable multiple of the sample rate frequency supplied on the word select
pin IIS_WS (= IIS_WS1). The clock generated by this so called WS_PLL is available for the user at pin SYSCLK.
Tables 3 and 4 show the I
2
C-bus settings needed to generate the n
×
f
s
clock. The memory map of the I
2
C-bus bits is
shown in Table 10.
Table 3
Word select input range selection
Table 4
Selection of n
×
f
s
clock at SYSCLK output
CLOCK INPUT (MHz)
pll_div[4:0]
N
DSP_TURBO
DIV_CLK_IN
DSP_CLOCK
(MHz)
8.192 (32 kHz
×
256)
9.728 (38 kHz
×
256)
11.2896 (44.1 kHz
×
256)
12.288 (48 kHz
×
256)
16.384 (32 kHz
×
512)
18.432 (32 kHz
×
576)
19.456 (38 kHz
×
512)
24.576 (96 kHz
×
256)
10H
09H
03H
00H
10H
0BH
09H
00H
272
227
198
181
272
244
227
181
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
69.632
69.008
69.854
69.504
69.632
68.544
69.008
69.504
SAMPLE RATE OF f
s
(kHz)
32 to 50
50 to 96
sel_loop_div[1:0]
01
00
sel2
sel1
sel0
SYSCLK (n
×
IIS_WS1)
512
DUTY FACTOR
1
0
0
50% for 32 to 50 kHz input; 66%
for 50 to 96 kHz input
50%
50%
50%
50%
0
0
0
0
1
1
0
0
1
0
1
0
384
256
192
128