1) Waveform Timing

Line timing[3K]

This is just an example of the timing. Different books give different figures !

2) Frame Sync

Frame pulses [11K]

3) Matching display line to bitmap line

The following discription describes how the video signal line is extracted from a bitmap. You can skip this if you aren't interested how the software works.

Mapping bitmap to screen [3K]

In this project we shall attempt to map a bitmap (.BMP, .GIF, whatever) to the relevent picture line. By comparing a bitmap (B) with the interlaced TV picture (A), we can see that bitmap line 1 (L1) is TV line O1, L2 is E2, L3 is O2, L4 is E2, etc. In turn we can campare fig2 (A) with fig1 and get a mapping between the bitmap line and the line number of the 405 line signal :-

Bitmap Line(Fig2B) TV Screen (Fig2A) Signal Line (Fig1)
L1 O1 216
L2 E1 14
L3 O2 217
L4 E2 15
L5 O3 218
| | |
L377 O189 404
L378 E189 202

We can now describe each signal line in terms of a source bitmap and sync lines :-

0..3 Pairs of vertical sync pulses
4..13 Normal sync but with video at black level
14 Line 2 of bitmap
15 Line 4 of bitmap
| |
201 Line 376 of bitmap
202 First half of bitmap line 378 plus one vertical sync
203..205 Pairs of verical sync pulses
206 One vertical sync foolowed by second half of bitmap line 1
207 Line 3 of bitmap
208 Line 5 of bitmap
| |
403 Line 375 of bitmap
404 Line 377 of bitmap

Next page : Encoding the EPROM Data

Page copyright
J.Evans 2002
Last updated
27th July 2002