Texas Instruments TMS320C3 Series, User Manual, Page: 51 / 166

TLC32040 AIC Initialization
4-17 Functional Overview
To ensure that the switched-capacitor lowpass and bandpass filters meet their
transfer function characteristics, the frequency of the clock inputs of the
switched-capacitor filter must be 288 kHz; otherwise, the upper and lower cut-
off frequencies of the low-pass and band-pass are scaled accordingly.
Equation 4–2 shows the switched capacitor filter frequency,
Equation 4–2. Switched Capacitor Filter Frequency
SCF Clock frequency
MCLK
A
_ _
=
2
For example, using this equation for an 8-kHz sampling rate with a MCLK of
6.25 MHz, results in a Tx counter A of 11 [A = MCLK/(2
SCF)]. Using
Equation 4–2, Tx counter B results in 36 [B = MCLK/(2 A Conver-
sion_Frequency)].
To initialize the AIC’s Tx counter A and B registers, you must send a primary
communication followed by a secondary communication (explained in the
Pri-
mary communications subsection below, and Secondary communications
subsection, on page 4-18.) Primary communications load values into the D/A
while secondary communications load A/D internal registers, such as the con-
trol register, Tx counters A and B, and Rx counters A and B.
Primary communications
Primary communications have a data value in the 14 MSBs (D15–D2) of data
and a mode selection in the two LSBs (D1–D0). This format is shown in
Figure 4–7.
Figure 4–7. Primary Communication Data Format
ÁÁÁ
ÁÁÁ
D15
ÁÁ
ÁÁ
D14
ÁÁÁ
ÁÁÁ
D13
ÁÁÁ
ÁÁÁ
D12
ÁÁÁ
ÁÁÁ
D11
ÁÁÁ
ÁÁÁ
D10
ÁÁ
ÁÁ
D9
ÁÁÁ
ÁÁÁ
D8
ÁÁÁ
ÁÁÁ
D7
ÁÁÁ
ÁÁÁ
D6
ÁÁÁ
ÁÁÁ
D5
ÁÁ
ÁÁ
D4
ÁÁÁ
ÁÁÁ
D3
ÁÁÁ
ÁÁÁ
D2
ÁÁÁ
ÁÁÁ
D1
ÁÁÁ
ÁÁÁ
D0
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Á ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Á
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
D/A converter value
ÁÁÁÁÁ
Á ÁÁÁ Á
ÁÁÁÁÁ
mode
selection
The AIC sends the data value to the D/A converter and enables one of the
modes shown in Table 4–2 depending on the two LSBs.