LC72720YV(2013) データシートの表示（PDF） - ON Semiconductor

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LC72720YV
(Rev.:2013)

Single-Chip RDS Signal-Processing System IC

ON Semiconductor 

DO pin operation

LC72720YV

This IC incorporates a RAM data buffer that can hold up to 24 blocks of data. At the point when one block of data is

written to this RAM, the IC issues a read request by switching the DO pin from high to low.

The DO pin always goes high for a fixed period (Tdo = 265 μs) after a readout and CE goes low. When all the data in

the data buffer has been read out, the DO pin is held in the high state until a new block of data has been written to the

RAM. If there is data that has not yet been read remaining in the data buffer, the DO pin goes low after the Tdo time has

elapsed.

After a synchronization reset, the DO pin is held high until synchronization is established. It goes low at the point the IC

synchronizes.

 When the DO pin is high following the 265 μs period (Tdo) after data is read out.

Here, the buffer is in the empty state, i.e. the state where new data has not been written. After this, when the DO pin

goes low, applications are guaranteed to be able to read out that data without it being overwritten by new data if they

start a readout operation within 480 ms of DO going low.

Tdo

CE pin

DO pin

T

(Last data)-1

Last data

New data

DO check (Tdo < T)

 When DO goes low 265 μs after data is read out

Here, there is data that has not been read out remaining in the data buffer. In this case, applications are guaranteed to

be able to read out that data without it being overwritten by new data if they start a readout operation within 20 ms

of DO going low. (Note that this is the worst case condition.)

Tdo

CE pin

DO pin

T

(Last data)-2

(Last data)-1

Last data

DO check (Tdo < T)

Notes : 1. Although an application can determine whether or not there is data remaining in the buffer by checking the DO level

with the above timing, checking the RE and RF flags in the serial data is a preferable method.

2. Applications are not limited to reading out one block of data at a time, but rather can read out multiple blocks of data

continuously as described above. When using this method, if an application references the RE and RF flags in the data

while reading out data, it can determine the amount of data remaining. However, the length of the period for data readout

(the period the CE pin remains high) must be kept under 20 ms.

3. If the DO pin is shared with other ICs that use the CCB interface, the application must identify which IC issued the

readout request. One method is to read out data from the LC72720YV and either check whether meaningful data has

been read (if the LC72720YV is not requesting a read, data consisting of all zeros will be read out) or check whether the

DO level goes low within the 256 μs following the completion of the read (if the DO pin goes low, then the request was

from another IC).

No. 6488-17/18

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