TLC32040C, TLC32040I, TLC32041C, TLC32041I

ANALOG INTERFACE CIRCUITS

SLAS014E – SEPTEMBER 1987 – REVISED MAY 1995

14

POST OFFICE BOX 655303

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 very careful not to violate this

requirement (see following diagram).

Frame Sync

FSX or FSR

t1

t2

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 may 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

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

t2

Transmit Conversion Period

Receive

Conversion

Period A

Receive

Conversion

Period B

FSX

FSR