TLC32044C Datasheet, PDF (14/39 Pages) Texas Instruments – VOICE-BAND ANALOG INTERFACE CIRCUITS

TLC32044C, TLC32044E, TLC32044I, TLC32044M, TLC32045C, TLC32045I
VOICE-BAND ANALOG INTERFACE CIRCUITS
SLAS017F – MARCH 1988 – REVISED MAY 1995
improper operation due to conversion times being too close together
If the difference between two successive D/A conversion frame syncs is less than 1/19.2 kHz, the AIC operates
improperly. In this situation, the second D/A conversion frame sync occurs too quickly and there is not enough
time for the ongoing conversion to be completed. This situation can occur if the A and B registers are improperly
programmed or if the A + A’ register or A – A’ register result is too small. When incrementally adjusting the
conversion period via the A + A’ register options, the designer should be careful not to violate this requirement
(see following diagram).
t1
t2
Frame Sync FSX
or
FSR
Ongoing
Conversion
 t2 – t1 1/19.2 kHz
asynchronous operation — more than one receive frame sync occurring between two transmit
frame syncs
When incrementally adjusting the conversion period via the A + A’ or A – A’ register options, a specific protocol
is followed. The command to use the incremental conversion period adjust option is sent to the AIC during a
FSX frame sync. The ongoing conversion period is then adjusted. However, either receive conversion period
A or B can be adjusted. For both transmit and receive conversion periods, the incremental conversion period
adjustment is performed near the end of the conversion period. Therefore, if there is sufficient time between
t₁ and t₂, the receive conversion period adjustment is performed during receive conversion period A. Otherwise,
the adjustment is performed during receive conversion period B. The adjustment command only adjusts one
transmit conversion period and one receive conversion period. To adjust another pair of transmit and receive
conversion periods, another command must be issued during a subsequent FSX frame (see figure below).
t1
FSX
FSR
Transmit Conversion Period
t2
Receive Conv.
Period A
Receive Conv.
Period B
Figure 2. Adjusted Transmit and Receive Conversion Periods
asynchronous operation — more than one transmit frame sync occurring between two receive
frame syncs
When incrementally adjusting the conversion period via the A + A’ or A – A’ register options, a specific protocol
is followed. For both transmit and receive conversion periods, the incremental conversion period adjustment
is performed near the end of the conversion period. The command to use the incremental conversion period
adjust options is sent to the AIC during a FSX frame sync. The ongoing transmit conversion period is then
adjusted. However, three possibilities exist for the receive conversion period adjustment in the diagram as
shown in the following figure. If the adjustment command is issued during transmit conversion period A, receive
conversion period A is adjusted if there is sufficient time between t₁ and t₂. If there is not sufficient time between
t₁ and t₂, receive conversion period B is adjusted. The receive portion of an adjustment command can be
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