Composite Video Details - FIGnition FUZE Hardware Reference Manual

Table of Contents

Advertisement

Fig 3.7
Generating A Text Screen. FIGnition FUZE uses 25x24 = 600 bytes of internal RAM for
display memory, and each byte contains a character not a bit pattern. The bit patterns are
stored in the AVR's internal Flash memory starting at the location kChrSet. There are 8
bit-pattern bytes per character. To display each bit pattern the firmware looks up the char-
acter code byte in video memory according to the current row and column; then looks up
the bit pattern at
kChrSet+8*TheCharacterCode+(ScanLine mod
8). If the charac-
ter code was <16, then it looks up the bit pattern from the UDG memory. If bit 7 of the
character code was set, the bit pattern is inverted [Fig 3.7, top half]. After all this, the bit
pattern is sent to the serial port, by storing the bit pattern at location $C6.

3.2.4 Composite Video Details

Each scan line is almost as simple as described earlier except that after the HSync pulse
there is a 4µs gap for what is called the colour burst, which FIGnition ignores.
Vertical sync however, is complex; complex enough for most websites to get it wrong. Fig
3.4 shows the true standard for PAL Vertical Sync; shown as a single sequence from the
end of one frame to the beginning of the next for even frames.
Vertical Sync is composed of 15 x 32µs periods. The First 5 contain 2µs pulses in each
32µs period. The next 5 contain 30µs pulses in each 32µs period and finally the last 5 con-
tain 2µs pulses in each 32µs period.
This description of composite video provides 312.5 scan lines at 50Hz, but a full imple-
mentation of the PAL video standard provides 625 lines at 25Hz. It does this using a tech-
nique called 'interlacing'. The video is divided into odd and even frames; and the scan lines
of the even frames are shown between those of the odd frames. To distinguish the two, the

Advertisement

Table of Contents
loading
Need help?

Need help?

Do you have a question about the FUZE and is the answer not in the manual?

Table of Contents