STV-6410-R01 datasheet(28/105 Pages) STMICROELECTRONICS

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VV5410 & VV6410

Digital Video Interface Format

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5-wire mode data is output on D[4:0].

Multiplexed with the sampled pixel data is control information including both video timing references, sensor status/configuration

data and the pixel average from the current line.

Video timing reference information takes the form of field start characters, line start characters, end of line characters and a line

counter.

Where hexadecimal values are used, they are indicated by a subscript H, such as FFH; other values are decimal.

8.2

Embedded control data

To distinguish the control data from the sampled video data all control data is encapsulated in embedded control sequences.

These are 6 bytes long and include a combined escape/sync character sequence, 1 control byte (the ‘command byte’) and 2

bytes of supplementary data.

To minimise the susceptibility of the embedded control data to random bit errors redundant coding techniques have been used to

allow single bit errors in the embedded control words to be corrected. However, more serious corruption of control words or the

corruption of escape/sync characters cannot be tolerated without loss of sync to the data stream. To ensure that a loss of sync is

detected a simple set of rules has been devised. The four exceptions to the rules are outlined below:

1. Data containing a command word that has two bit errors.

2. Data containing two ‘end of line’ codes that are not separated by a ‘start of line’ code.

3. Data preceding an ‘end of ﬁeld’ code before a start of frame’ code has been received.

4. Data containing line that do not have sequential line numbers (excluding the ‘end of ﬁeld’ line).

If the host detects one of these violations then it should abandon the current field of video

8.2.1

The combined escape and sync character

Each embedded control sequence begins with a combined escape and sync character that is made up of three words. The first

two of these are FFH FFH- constituting two words that are illegal in normal data. The next word is 00H - guaranteeing a clear

signal transition that allows a host to determine the position of the word boundaries in the serial stream of nibbles. Combined

escape and sync characters are always followed by a command byte - making up the four byte minimum embedded control

sequence.

8.2.2

The command word

The byte that follows the combined escape/sync characters defines the type of embedded control data. Three of the 8 bits are

used to carry the control information, four are ‘parity bits’ that allow the host to detect and correct a certain level of errors in the

transmission of the command words, the remaining bit is always set to 1 to ensure that the command word never has the value

00H. The coding scheme used allows the correction of single bit errors (in the 8-bit sequence) and the detection of 2 bit errors

The three data bits of the command word are interpreted as shown in Figure 13.The even parity bits are based on the following

relationships:

1. An even number of ones in the 4-bit sequence (C2, C1, C0 and P0).

2. An even number of ones in the 3-bit sequence (C2, C1, P1).

3. An even number of ones in the 3-bit sequence (C2, C0, P2).

4. An even number of ones in the 3-bit sequence (C1, C0, P3).

Table 13 shows how the parity bits maybe used to detect and correct 1-bit errors and detect 2-bit errors.

8.2.3

Supplementary Data

The last 2 bytes of the embedded control sequence contains supplementary data. The are two options:

1. The last 2 bytes of the SAV 6 byte sequence contain the current 12-bit line number. The 12-bit line number is packaged up

by splitting it into two 6-bit values. Each 6-bit value is then converted into an 8-bit value by adding a zero to the start and an

odd word parity bit at the end.

2. The 5th byte of the EAV sequence contains a pixel average for that line either based upon the middle 256 pixels if the

CIF,PAL or NTSC video modes are selected or the middle 128 pixels if the QCIF video mode is selected. The ﬁnal byte is

FFH.

Note: in 5-wire mode, the embedded control data is calculated as detailed above and output as the most significant 8-bits. The

least significant 2-bits are padded with zero.

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