1.0 Functional Description
CX25870/871
1.3 Device Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3.46 TV Auto-Detection Procedures
The device can determine whether or not the DAC output is connected to a
monitor by verifying that the output is doubly-terminated. The MONSTATx bit
for the corresponding DAC is set to a 1 if the device senses a doubly-terminated
load on a reset condition or if the CHECK_STAT register bit is set. While
CHECK_STAT is set, the output is forced to 2/3 of VREF when terminated and
4/3 of VREF if unterminated. The MONSTATx bit reflects the condition when the
DAC output is less than or equal to VREF. The CHECK_STAT bit is
automatically cleared after two clock cycles.
The CX25870/871 can be read from using 2 different methods. The first
method is called Standard serial read-back. To perform a read, simply have the
master device issue the CX25870/871’s serial device address (0x89 or 0x8B
depending on the state of the encoders ALTADDR pin), transmit the particular
subaddress (encoder register index) to read from, and then wait for the
CX25870/871 to transmit the appropriate 8-bits of data. Of course, START and
STOP conditions and ACKs must exist at the pertinent times as well, but this
summarizes the basic procedure.
The second method that can be used to read back from the encoder is called
the Legacy method. This is because the procedure that follows was the only
manner in which Conexant’s first generation encoder (i.e., Bt868/869) could be
read from. For compatibility purposes, this method was carried forward and exists
in this second generation encoder.
The Legacy procedure to follow for serial read-back and TV detection purposes
is:
1. Write 01 to the ESTATUS[1:0]{bits D7=msb and D6 of register 0xC4}bit
field. This sets up the encoder to read the MONSTAT data and check if the
DACs have a TV connected.
2. Write the CHECK_STAT register bit to a one (bit D6 of register BA). This
will latch the MONSTAT data internally and then clear itself.
3. Wait 600 µs to allow the analog nodes to reach their operating point.
4. Read the MONSTAT data by issuing 0x89 or 0x8B for the CX25870/871’s
device address. This ensures the least significant bit of the device write
portion of the transaction is 1, which indicates to the encoder that it must
send a byte of data on the next serial transaction. Do not write a subaddress
to the encoder (this is not necessary since the first generation encoder only
had one read register) and then read the next byte after the ACK. The 8-bit
read in Step 1 contains either the CX25870’s ID&VERSION (if ESTATUS
was written to 00) or the CX25870’s Monitor Detection for DACs C, B,
and A + Closed Caption Status info and the FIELD # (if ESTATUS = 01).
If ESTATUS was written to 10 in Step 1, the read byte will contain the
PLL_LOCK, FIFO status bits, PAL bit, and BUSY bit.
1-88
Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
