STV6404E-001 datasheet(9/54 Pages) STMICROELECTRONICS

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VV5404 & VV6404

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Digital Video Interface Format

4.1

General description

The video interface consists of a unidirectional, tri-stateable 4-wire databus. The nibble transmission is synchronised

to the rising edge of the system clock (Figure 13).

Digital video data is 8 bits per sample, transmitted as serial pairs of parallel 4-bit nibbles (most significant nibble first)

on 4 wires.

Multiplexed with the sampled pixel data is control information including both video timing references and sensor

status/configuration data. 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.

4.2

Embedded control data

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

sequences. These are a minimum of 6 words long and includes a combined escape/sync character, 1 control word

(the ‘command byte’) and 2 words 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 words 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 frame’ 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 frame’ line).

If the video processor detects one of these violations then it should abandon the current frame of video.

4.2.1 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 video processor 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 word -

making up the four word minimum embedded control sequence.

4.2.2

The command word

The word 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 video processor 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 is 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 5.

Read-out Order

Progressive Scan (Non-interlaced)

Form of encoding

Uniformly quantised, PCM, 8 bits per sample

Correspondence between video

signal levels and quantisation

levels:

Internally valid pixel data is clipped to ensure that 00H and FFH

values do not occur when pixel data is being output on the data

bus. This gives 254 possible values for each pixel (1 - 254). The

video black level corresponds to code 16.

Table 5 : Video encoding parameters

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