DSPIC30F5011_07 Datasheet, PDF (125/224 Pages) Microchip Technology – High-Performance, 16-bit Digital Signal Controllers

dsPIC30F5011/5013
18.3.7 BIT CLOCK GENERATOR
The DCI module has a dedicated 12-bit time base that
produces the bit clock. The bit clock rate (period) is set
by writing a non-zero 12-bit value to the BCG<11:0>
control bits in the DCICON3 SFR.
When the BCG<11:0> bits are set to zero, the bit clock
will be disabled. If the BCG<11:0> bits are set to a non-
zero value, the bit clock generator is enabled. These
bits should be set to ‘0’ and the CSCKD bit set to ‘1’ if
the serial clock for the DCI is received from an external
device.
The formula for the bit clock frequency is given in
Equation 18-2.
EQUATION 18-2: BIT CLOCK FREQUENCY
FCY
FBCK =
2 _• (BCG + 1)
The required bit clock frequency will be determined by
the system sampling rate and frame size. Typical bit
clock frequencies range from 16x to 512x the converter
sample rate depending on the data converter and the
communication protocol that is used.
To achieve bit clock frequencies associated with com-
mon audio sampling rates, the user will need to select
a crystal frequency that has an ‘even’ binary value.
Examples of such crystal frequencies are listed in
Table 18-1.
TABLE 18-1: DEVICE FREQUENCIES FOR COMMON CODEC CSCK FREQUENCIES
FS (KHZ)
FCSCK/FS
FCSCK (MHZ)⁽¹⁾
FOSC (MHZ)
PLL
FCYC (MIPS)
BCG⁽²⁾
8
256
2.048
8.192
4
8.192
1
12
256
3.072
6.144
8
12.288
1
32
32
1,024
8.192
8
16.384
7
44.1
32
1.4112
5.6448
8
11.2896
3
48
64
3.072
6.144
16
24.576
3
Note 1: When the CSCK signal is applied externally (CSCKD = 1), the external clock high and low times must
meet the device timing requirements.
2: When the CSCK signal is applied externally (CSCKD = 1), the BCG<11:0> bits have no effect on the
operation of the DCI module.
© 2007 Microchip Technology Inc.
DS70116G-page 123