TDA7546 datasheet(34/68 Pages) STMICROELECTRONICS

34 / 68 page

Functional description

TDA7546

34/68

The RAM buffer is used as a circular FIFO (Figure 9). If more than 24 blocks are written, the

oldest data will be overwritten. One level of the buffer consists of 4 bytes (2 information

bytes, 2 RDS data bytes). If less than 4 bytes of the RAM buffer are read out from the

master via the SPI or I2C interface, the buffer address will not be incremented.

Figure 10.

RAM buffer states

The different states of the buffer are indicated with the help of following flags:

–

“bne”, buffer not empty. It is set as soon as one RDS block is written in

the buffer, and reset when reading rds_int register. This flag is a bit of

rds_int register, it is also an interrupt source .

–

“bfull”, buffer full. It is set when 24 RDS blocks have been written, that is

to say that there is about 20 ms to read out the buffer content before an

overflow occurs. This flag is an interrupt source.

–

“bovf”, buffer overflow. It is set if more than 24 RDS blocks are written.

This flag is a bit of register rds_corrp (refer to Table 39) and is cleared

only by reading the whole buffer (24 blocks).

bne = 0

bfull = 0

bovf = 0

the read pointer reaches but

doesn't go ahead the write pointer

the read pointer doesn't go

ahead the write pointer

bne = 1

bfull = 0

bovf = 0

bne = 0

bfull = 0

bovf = 0

the write pointer reaches position

before the read pointer

(24 data written before any read)

the Wp reaches Rp

overflow flag is set

and the first data is

overwritten

bne = 1

bfull = 0

bovf = 0

bne = 1

bfull = 1

bovf =

Rp Wp

reset status

write next three data into

buffer (internally)

bne = 1

bfull = 0

bovf = 0

read three data from buffer

(externally)

bne = 1

bfull = 0

bovf = 0

Note : The read pointer Rp is driven externally through micro read access,

and the write pointer Wp is driven internally on every incoming block.

write

bne = 1

bfull = 1

bovf = 01

write

Wp and Rp are

moving together

overwriting next data

read

bne = 0

bfull = 0

bovf = 0

Rp Wp

write the first data

into buffer (internally)

write

read

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