Datasheet

ADV7188
Rev. A | Page 80 of 112
MPU PORT DESCRIPTION
The ADV7188 supports a 2-wire (I
2
C-compatible) serial inter-
face. Two inputs, serial data (SDA) and serial clock (SCLK),
carry information between the ADV7188 and the system I
2
C
master controller. Each slave device is recognized by a unique
address. The ADV7188’s I
2
C port allows the user to set up and
configure the decoder and then to read back captured VBI data.
The ADV7188 has four possible slave addresses for both read
and write operations, depending on the logic level on the ALSB
pin. These four unique addresses are shown in
Table 103. The
ADV7188’s ALSB pin controls Bit 1 of the slave address. By
altering the ALSB, it is possible to control two ADV7188s in an
application without having a conflict with the same slave
address. The LSB (Bit 0) sets either a read or write operation.
Logic 1 corresponds to a read operation; Logic 0 corresponds to
a write operation.
Table 103. I
2
C Address
ALSB R/
W
Slave Address
0 0 0x40
0 1 0x41
1 0 0x42
1 1 0x43
To control the device on the bus, a specific protocol must be
followed. First, the master initiates a data transfer by establishing a
start condition, which is defined by a high-to-low transition on
SDA while SCLK remains high. This indicates that an address/data
stream follows. All peripherals respond to the start condition
and shift the next eight bits (7-bit address + R/
W
bit). The bits
are transferred from MSB down to LSB. The peripheral that
recognizes the transmitted address responds by pulling the
data line low during the ninth clock pulse; this is known as an
acknowledge bit. All other devices withdraw from the bus at
this point and maintain an idle condition. The idle condition is
where the device monitors the SDA and SCLK lines, waiting for
the start condition and the correct transmitted address.
The R/
W
bit determines the direction of the data. If the first
byte of the LSB is Logic 0, the master writes information to the
peripheral. If the first byte of the LSB is Logic 1, the master reads
information from the peripheral.
The ADV7188 acts as a standard slave device on the bus. The
data on the SDA pin is eight bits long, supporting the 7-bit
addresses plus the R/
W
bit. The ADV7188 has 249 subaddresses
to enable access to the internal registers. It therefore interprets
the first byte as the device address and the second byte as the
starting subaddress. The subaddresses autoincrement, allowing
data to be written to or read from the starting subaddress. A
data transfer is always terminated by a stop condition. The user
can also access any subaddress register on a one-by-one basis
without updating all the registers.
Stop and start conditions can be detected at any stage during the
data transfer. If these conditions are asserted out of sequence with
normal read and write operations, they cause an immediate
jump to the idle condition. During a given SCLK high period,
the user should issue only one start condition, one stop condition,
or a single stop condition followed by a single start condition. If
an invalid subaddress is issued by the user, the ADV7188 does
not issue an acknowledge and returns to the idle condition.
If the highest subaddress is exceeded in autoincrement mode,
the following action is taken:
1.
During a read, the highest subaddress register contents
continue to be output until the master device issues a no
acknowledge. This indicates the end of a read. In a no
acknowledge condition, the SDA line is not pulled low on
the ninth pulse.
2.
During a write, the data for the invalid byte is not loaded into
a subaddress register. Instead, a no acknowledge is issued
by the ADV7188, and the part returns to the idle condition.
05478-049
SDATA
SCLOCK
START ADDR ACK ACK DATA ACK STOPSUBADDRESS
1–7 1–78 9 8 9 1–7 8 9
S P
R/W
Figure 46. Bus Data Transfer
05478-050
S
WRITE
S
EQUENCE
SLAVE ADDR A(S) SUB ADDR A(S) DATA A(S)
DATA A(S) P
S
READ
S
EQUENCE
SLAVE ADDR SLAVE ADDRA(S) SUB ADDR A(S) S A(S) DATA A(M)
DATA A(M) P
S = START BIT
P = STOP BIT
A(S) = ACKNOWLEDGE BY SLAVE
A(M) = ACKNOWLEDGE BY MASTER
A(S) = NO ACKNOWLEDGE BY SLAVE
A(M) = NO ACKNOWLEDGE BY MASTER
LSB = 1LSB = 0
Figure 47. Read and Write Sequence