HMP8156ACN Intersil, HMP8156ACN Datasheet - Page 15

• Manufacturer Part Number: HMP8156ACN
• Description: NTSC/PAL Encoder 64-Pin MQFP
• Manufacturer: Intersil

Specifications of HMP8156ACN

• Package: 64MQFP
• Operating Temperature: 0 to 70 °C

Chrominance Modulation
The HMP8154/HMP8156A uses a numerically controlled
oscillator (NCO) clocked by CLK2 and a sine look up ROM to
generate the color subcarrier. The subcarrier from the ROM is
pre-scaled to generate the proper levels for the various video
standards. Prescaling outside the CbCr data path minimizes
color processing artifacts. The HMP8154/HMP8156A
modulates the filtered 8:8:8 chrominance data with the
synthesized subcarrier.
Subcarrier Phase
The SCH phase is 0 degrees after reset but then changes
monotonically over time due to residue in the NCO. In an
ideal system, zero SCH phase would be maintained forever.
In reality, this is impossible to achieve due to pixel clock
frequency tolerances.
If enabled, the HMP8154/HMP8156A resets the NCO
periodically to avoid an accumulation of SCH phase error.
The reset occurs at the beginning of each field to burst
phase sequence. The sequence repeats every 4 fields for
NTSC or 8 fields for PAL.
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
-10
-20
-30
-40
-50
-60
FIGURE 19. Cb AND Cr LOWPASS FILTER RESPONSE
0
0
0
0
0.2
FIGURE 19A. FULL SPECTRUM
1
NTSC OR PAL
RECTANGULAR PIXEL
CLK2 = 27.00MHz
FIGURE 19B. PASS BAND
0.4
NTSC SQUARE PIXEL
CLK2 = 24.54MHz
2
FREQUENCY (MHz)
FREQUENCY (MHz)
NTSC OR PAL
RECTANGULAR PIXEL
CLK2 = 27.00MHz
NTSC SQUARE PIXEL
CLK2 = 24.54MHz
0.6
15
0.8
3
1.0
PAL SQUARE PIXEL
CLK2 = 29.50MHz
PAL SQUARE PIXEL
CLK2 = 29.50MHz
4
1.2
5
HMP8154, HMP8156A
1.4
1.6
6
Resetting the SCH phase every four fields (NTSC) or eight
fields (PAL) avoids the accumulation of SCH phase error at
the expense of requiring any NTSC/PAL decoder after the
encoder be able to handle very minor “jumps” (up to 2
the SCH phase at the beginning of each four-field or eight-
field sequence. Most NTSC/PAL decoders are able to
handle this due to video editing requirements.
Composite Video Limiting
The HMP8154/HMP8156A adds the luminance and modulated
chrominance together with the sync, color burst, and optional
blanking pedestal to form the composite video data. If enabled
in the video processing register, the encoder limits the active
video so that it is always greater than one-eighth of full scale.
This corresponds to approximately one-half the sync height.
This allows the generation of “safe” video in the event
nonstandard YCbCr values are input to the device.
Closed Captioning
If enabled in the auxiliary data control register, the
HMP8154/HMP8156A generates closed captioning data on
specified scan lines. The captioning data stream includes clock
run-in and start bits followed by the captioning data. During
closed captioning encoding, the pixel and overlay inputs are
ignored on the scan lines containing captioning information.
The HMP8154/HMP8156A has two 16-bit registers containing
the captioning information. Each 16-bit register is organized as
two cascaded 8-bit registers. One 16-bit register (caption 21) is
read out serially during line 18, 21 or 22; the other 16-bit
register (caption 284) is read out serially during line 281, 284 or
335. The data registers are shifted out LSB first.
The bytes may be written in any order but both must be
written within one frame time for proper operation. If the
registers are not updated, the encoder resends the
previously loaded values.
The HMP8154/HMP8156A provides a write status bit for
each captioning line. The encoder clears the write status bit
to ‘0’ when captioning is enabled and both bytes of the
captioning data register have been written. The encoder sets
the write status bit to ‘1’ after it outputs the data, indicating
the registers are ready to receive new data.
Captioning information may be enabled for either line, both
lines, or no lines. The captioning modes are summarized in
Table 8.
Controlled Edges
The NTSC and PAL video standards specify edge rates and
rise and fall times for portions of the video waveform. The
HMP8154/HMP8156A automatically implements controlled
edge rates and rise and fall times on these edges:
1. Analog horizontal sync (rising and falling edges)
2. Analog vertical sync interval (rising and falling edges)
3. Color burst envelope
4. Blanking of analog active video
5. Overlay with internal mixing
6. Closed captioning information
August 20, 2009
FN4343.5
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