Texas Instruments TMS320C3 Series, User Manual, Page: 52 / 166

TLC32040 AIC Initialization
4-18
Table 4–2. Primary Communications Mode Selection
LSBs Mode
00 Tx Counter A
²
TA, Rx Counter A
²
RA
Tx Counter B
²
TB, Rx Counter B
²
RB
01 Tx Counter A
²
TA + TA’, Rx Counter A
²
RA + RA’
Tx Counter B
²
TB, Rx Counter B
²
RB
10 Tx Counter A
²
TA - TA’, Rx Counter A
²
RA + RA’
Tx Counter B
²
TB, Rx Counter B
²
RB
11 Tx Counter A
²
TA, Rx Counter A
²
RA
Tx Counter B
²
TB, Rx Counter B
²
RB
The second and third modes use the TA’ and RA’ registers to advance or slow
down the sampling frequency by shortening or lengthening the sample period.
This is particularly useful in modem applications. It can also enhance the sig-
nal-to-noise performance, perform frequency-tracking functions, and gener-
ate nonstandard modem frequencies.
Secondary communications
Secondary communication follows a primary communication that has the two
LSBs set to 11. This secondary communication programs the AIC by loading
the A, A’, B, or control registers. Figure 4–8 shows the secondary communica-
tion data format. The TA, RA, TB, and RB values are unsigned. The TA’ and
RA’ values are in signed 2s-complement format. The control register enables
and disables auxiliary inputs, bandpass filters, and so forth.
Figure 4–8. Secondary Communication Data Format
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
X X TA register value (unsigned) X X RA register value (unsigned) 0 0
X
TA’ register value (signed 2s
complement) X
RA’ register value (signed 2s
complement) 0 1
X TB register value (unsigned) X RB register value (unsigned) 1 0
X X X X X X X X Control register 1 1