2004 Mar 01
15
Philips Semiconductors
Product specification
Digital video encoder
SAA7102; SAA7103
Only vertical frequencies of 50 and 60 Hz are allowed with
the SAA7102; SAA7103. In slave mode, it is not possible
to lock the encoders colour carrier to the line frequency
with the PHRES bits.
In the (more common) master mode, the time base of the
circuit is continuously free-running. The IC can output a
frame sync at pin FSVGC, a vertical sync at pin VSVGC, a
horizontal sync at pin HSVGC and a composite blanking
signal at pin CBO. All of these signals are defined in the
PIXCLK domain. The duration of HSVGC and VSVGC are
fixed, they are 64 clocks for HSVGC and 1 line for VSVGC.
The leading slopes are in phase and the polarities can be
programmed.
The input line length can be programmed. The field length
is always derived from the field length of the encoder and
the pixel clock frequency that is being used.
CBO acts as a data request signal. The circuit accepts
input data at a programmable number of clocks after CBO
goes active. This signal is programmable and it is possible
to adjust the following (see Figs 12 and 13):
•
The horizontal offset
•
The length of the active part of the line
•
The distance from active start to first expected data
•
The vertical offset separately for odd and even fields
•
The number of lines per input field.
In most cases, the vertical offsets for odd and even fields
are equal. If they are not, then the even field will start later.
The SAA7102; SAA7103 will also request the first input
lines in the even field, the total number of requested lines
will increase by the difference of the offsets.
As stated above, the circuit can be programmed to accept
the look-up and cursor data in the first 2 lines of each field.
The timing generator provides normal data request pulses
for these lines; the duration is the same as for regular lines.
The additional request pulses will be suppressed with
LUTL set to logic 0; see Table 105. The other vertical
timings do not change in this case, so the first active line
can be number 2, counted from 0.
7.16
I
2
C-bus interface
The I
2
C-bus interface is a standard slave transceiver,
supporting 7-bit slave addresses and 400 kbits/s
guaranteed transfer rate. It uses 8-bit subaddressing with
an auto-increment function. All registers are write and
read, except two read only status bytes.
The register bit map consists of an RGB Look-Up Table
(LUT), a cursor bit map and control registers. The LUT
contains three banks of 256 bytes, where each RGB triplet
is assigned to one address. Thus a write access needs the
LUT address and three data bytes following subaddress
FFH. For further write access auto-incrementing of the
LUT address is performed. The cursor bit map access is
similar to the LUT access but contains only a single byte
per address.
The I
2
C-bus slave address is defined as 88H.
7.17
Programming the SAA7102; SAA7103
In order to program the SAA7102; SAA7103 it is first
necessary to determine the input and output field timings.
The timings are controlled by decoding binary counters
that index the position in the current line and field
respectively. In both cases, 0 means the start of the sync
pulse.
At 60 Hz, the first visible pixel has the index 256,
710 pixels can be encoded; at 50 Hz, the index is 284,
702 pixels can be visible. Some variables are defined
below:
•
InPix: the number of active pixels per input line
•
InPpl: the length of the entire input line in pixel clocks
•
InLin: the number of active lines per input field/frame
•
TPclk: the pixel clock period
•
OutPix: the number of active pixels per output line
•
OutLin: the number of active lines per output field
•
TXclk: the encoder clock period (37.037 ns).
The output lines should be centred on the screen. It should
be noted that the encoder has 2 clocks per pixel;
see Table 72.
ADWHS = 256 + 710
−
OutPix (60 Hz);
ADWHS = 284 + 702
−
OutPix (50 Hz);
ADWHE = ADWHS + OutPix
×
2 (all frequencies)
For vertical, the procedure is the same. At 60 Hz, the first
line with video information is number 19, 240 lines can be
active. For 50 Hz, the numbers are 23 and 287;
see Table 78.
(60 Hz);
(50 Hz);
LAL = FAL + OutLin (all frequencies)
FAL
19
240
OutLin
–
2
---------------------------------
+
=
FAL
23
287
OutLin
–
2
---------------------------------
+
=
