CSP1027 Datasheet, PDF (16/64 Pages) Agere Systems – CSP1027 Voice Band Codec for Cellular Handset and Modem Applications

CSP1027 Voice Band Codec for
Cellular Handset and Modem Applications
Data Sheet
December 1999
4 Architectural Information (continued)
4.5.2 Clock Divider 2
4.5 Clock Generation
Figure 17 on page 15 shows the clock generation and
distribution for the CSP1027. The programmable divid-
ers can customize the codec sample and master clock
rates for a variety of applications in addition to standard
8 kHz sampling, while allowing a range of values for
the crystal-controlled input clock. In Figure 17 on page
15, XOSCEN is a chip input to enable the crystal oscil-
lator circuit. XLO and XHI are the two leads for the
crystal. CLK is the chip clock input if the crystal is not
used. CKS is the internal codec sample clock, typically
8 kHz. CKOS is the internal codec oversampled clock,
typically 1 MHz. CKO1 and CKO2 are general-purpose
clocks brought out to chip pins. CDIV1 and CDIV2 are
programmable dividers with a range from 1 to 31.
CDIV0 is programmed to be 1 or 2, but extra clock
pulses can be added or subtracted at the output for one
period of time following a write to the control register
cioc1. This one-time increase or decrease in the num-
ber of clocks is programmed by ADJMOD and ADJ and
causes a phase shift in the CKO1 and CKS output. F1
is an integral or a fractional divider controlled by the
five programmable coefficients shown connected to it.
With the fractional divide, the period of CKOS will vary,
but the period of CKS will be constant.
The following discussion begins with the crystal oscilla-
tor and is followed by a detailed description of each
divisor block. Section 7.5 on page 45 provides some
examples of how to program the clocks.
4.5.1 Crystal Oscillator
The CSP1027 has a selectable on-chip clock oscillator.
A logic 1 on the XOSCEN pin enables the crystal oscil-
lator. A logic 0 disables the oscillator, powers it down,
and selects the input buffer connected to the CLK pin.
To use the oscillator, select a 20 MHz to 30 MHz funda-
mental-mode crystal with a series resistance less than
60 Ω and a mutual capacitance less than 7.0 pF. Con-
nect the crystal between the XLO and XHI pins, and
add 10 pF capacitors between XLO and ground, and
XHI and ground. The XOSCEN pin enables and dis-
ables the crystal oscillator. See the application informa-
tion on optimizing the oscillator performance.
ICLK
÷CDIV2
CKO2
Figure 18. Clock Divider 2
5-7589 (F)
The CDIV2 field in cioc0 (see Table 7 on page 26) sets
the clock divider that generates the output clock,
CKO2. The clock output is a general-purpose clock that
can be used to clock external logic or processors.
CDIV2 ranges from 1 to 31, with 0 holding the output
low. RSTB going low sets CDIV2 to ÷16. CKO2 is
active while RSTB is low and synchronized by RSTB
going high.
4.5.3 Clock Divider 0
ADJMOD,
ADJ
ICLK
÷CDIV0
ICLK0
Figure 19. Clock Divider 0
5-7588 (F)
The CDIV0 field in cioc1 (see Table 8 on page 27) sets
the clock divider that generates the internal clock 0
(ICLK0) to either divide by one or divide by two. The
ADJMOD and ADJ fields in cioc1 are used to adjust
the phase of ICLK0 by increasing or decreasing the
rate of ICLK0 for a burst of pulses, one time only. This
event occurs each time control register cioc1 is written
with nonzero values of ADJ. For example, let CDIV0 be
set to ÷2, ADJ to seven, and ADJMOD to one
(advance). After this word is written to the cioc1 regis-
ter, seven ICLK0 pulses will occur at the same rate as
ICLK, not divided by two. These seven clock pulses
shift the phase of CKOS, CKS, and CKO1 earlier, thus
advancing these clocks. If ADJMOD is set to zero
(retard), the ÷2 becomes a ÷3 for seven pulses of
ICLK0. The CDIV0 clock divider is temporarily changed
internally so that it divides by one greater, to retard the
clocks, or one less, to advance the clocks, for the spec-
ified number of ICLK0 cycles. Note that the CDIV0
clock divider must be set to divide by two in order to
advance and retard the clocks. If CDIV0 clock divider is
set to divide by 1, one can only retard the clocks.
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