LMH0031 Datasheet, PDF (15/31 Pages) National Semiconductor (TI) – SMPTE 292M/259M Digital Video Deserializer Descrambler with Video and Ancillary Data FIFOs

Device Operation (Continued)
cally. EDH errors are reported in the EDH0, EDH1, and
EDH2 register sets of the configuration and control registers.
Updated or new EDH check words and flags may be gener-
ated and inserted in the data. EDH check words are gener-
ated using the polynomial X¹⁶ + X¹² + X⁶ + 1 per SMPTE
RP165. Generation and automatic insertion of new or cor-
rected EDH check words is controlled by EDH Force and
EDH Enable bits in the control registers. EDH check words
and status flags are inserted in the parallel data at the
correct positions in the Ancillary Data space and formatted
per SMPTE 291M. After a reset, the initial state of all EDH
and CRC check characters is 00h.
The SMPTE 292M high definition video standard employs
CRC (cyclic redundancy check codes) error checking in-
stead of EDH. The CRC consists of two 18-bit words gener-
ated using the polynomial X¹⁸ + X⁵ + X⁴ + 1 per SMPTE
292M. One CRC is used for luminance and one for chromi-
nance data. The CRCs appear in the data stream following
the EAV and line number characters. The CRCs are checked
and errors are reported in the EDH0, EDH1, and EDH2
register sets of the configuration and control registers.
PHASE-LOCKED LOOP / CLOCK-DATA RECOVERY
SYSTEM
The phase-locked loop and clock-data recovery (PLL/
CDR) system generates all internal timing and data rate
clocks for the LMH0031. The PLL/CDR system consists of
five main functional blocks: 1) the input buffer which receives
the incoming data, 2) input data samplers which oversample
the data coming from the input buffer, 3) a PLL (VCO, divider
chain, phase-frequency detector and internal loop filter)
which generates sampling and other system clocks, 4) a
digital CDR system to recover the oversampled serial input
data from the samplers and the digital system control and 5)
a rate detect controller which sequences the PLL to find the
data rate.
Using an oversampling technique, the timing information
encoded in the serial data is extracted and used to synchro-
nize the recovered clock and data. The parallel data rate and
other clock signals are derived from the regenerated serial
clock. The parallel data rate clock is 1/10th of the serial data
rate clock for standard definition or 1/20th of the serial data
clock frequency for high definition. The data interface be-
tween the CDR and the digital processing block uses 10-bit
data plus the required clocks.
The PLL is held in coarse frequency lock by an external
27MHz clock signal, EXT CLK, or by an external 27MHz
crystal and internal oscillator. Upon power-on, EXT CLK is
the default reference. The internal oscillator and an external
crystal may be used as the reference by setting the OSCEN
bit in the CDR register. The reference clock reduces lock
latency and enhances format and auto-rate detection robust-
ness. PLL acquisition, data phase alignment and format
detection time is 20ms or less at 1.485Mbps. The VCO has
separate V_DDPLL and V_SSPLL power supply feeds, pins 51
and 52, which may be supplied power via an external low-
pass filter, if desired.
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FIGURE 6. Crystal and Load Circuit
A 27MHz crystal and load circuit may be used to provide the
reference clock. A fundamental mode crystal with the follow-
ing parameters is used: frequency 27MHz, frequency toler-
ance ±30ppm, load capacitance 18pF, maximum drive level
100µW, equivalent series resistance <50Ω, operating tem-
perature range 0˚C to 70˚C. Refer to Figure 6 for a typical
load circuit and connection information.
The LMH0031 indicates that the PLL is locked to the incom-
ing data rate and that the CDR has acquired a phase of the
serial data by setting the Lock Detect bit in the Video Info 0
control register. Indication of the standard being processed
is retained in the FORMAT[4:0] bits in the FORMAT 1 con-
trol data register. Format data from this register can be
programmed for output on the multi-function I/O port. The
power-on default assigns Lock Detect as I/O Port bit 4.
POWER SUPPLIES, POWER-ON-RESET AND RESET
INPUT
The LMH0031 requires two power supplies, 2.5V for the core
logic functions and 3.3V for the I/O functions. The supplies
must be applied to the device in proper sequence. The 3.3V
supply must be applied prior to or coincident with the 2.5V
supply. Application of the 2.5V supply must not precede the
3.3V supply. It is recommended that the 3.3V supply be
configured or designed so as to control application of the
2.5V supply in order to satisfy this sequencing requirement.
The LMH0031 has an automatic, power-on-reset circuit.
Reset initializes the device and clears TRS detection cir-
cuitry, all latches, registers, counters and polynomial
generators/checkers and resets the EDH/CRC characters to
00h. An active-HIGH-true, manual reset input is available at
pin 49. The reset input has an internal pull-down device and
may be considered inactive when unconnected.
Important: When power is first applied to the device or
following a reset, the ancillary and Control Data Port must
be initialized to receive data. This is done by toggling A_CLK
three times.
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