The PRACTEL PT-430, were developed in the early 1990s for the Australian broadcast industry, and primarily used in (ENG) Electronic News Gathering to provide a constant video and audio between the station over a microwave link.
Front |
Rear |
Video Board |
Audio/switcher board |
This project showcases my successful reverse engineering of the code stored in the EPROM of the PT-430. I developed a C program capable of regenerating both the test patterns and the ID text overlays, allowing for personalized test patterns and identification text on the PT-430 generator.
A handful of PT-430 generators are still in use, proving that not all classic tech has faded away! Thanks to this work, the PT-430 continues to be a valuable tool for amateur television (ATV) enthusiasts. While the 4:3 PAL BG format may seem "old school," there are still scenarios where its CVBS output can be converted to DVB using affordable converters.
I have a special appreciation for the SAA1043 and SAA1044 Philips sync generator and subcarrier coupler chips. These components were renowned for their use in high-end cameras and studio-grade sync pulse generators—a testament to their quality and reliability.
The reverse engineering journey has sharpened my understanding of memory addressing and embedded systems. I’ve also created a C program that runs on both Windows and Linux (though the Linux build is still awaiting its first test). This ongoing project continues to challenge and expand my technical abilities.
Here’s your content, clearly structured and enhanced in Markdown for readability:
The original EPROM program for the PT-430 was likely written in GW-BASIC. Unfortunately, the disk containing the source code is now “un-obtainium”—it’s probably lost forever, possibly tucked away with an old DOS 6.1 disk set!
- The PT-430 generator produces three working patterns in a 4:3 aspect ratio:
- Color Black
- Color Bars
- Pulse-and-Bar test patterns
- Both the Color Bars and Pulse-and-Bar patterns feature a center-aligned station ID.
- My program generates four patterns—however, the 4th pattern can't be displayed without modifying the hardware. The original uses a center-off toggle switch; replacing it with a 4-position selector switch unlocks the 4th pattern for free!
- After dumping the EPROM hex code and studying the schematic, I found:
- The PT-430 can generate primary/secondary adaptive colors from
0x00(Black) up to0x0F(White). - Pattern combinations are determined by the lower nibble (
D0toD3) on the EPROM data lines.
- The PT-430 can generate primary/secondary adaptive colors from
📄 Reference: PT-430 schematic
- Cascaded 4-bit counters (
74HC393) count 7 bits horizontally.- This clocks out the same line for 128 pixels.
- At line 140, a 4-bit binary up counter (
CD4520) takes over, clocking out 16 lines:- Odd/even lines display either color bars or color black.
- Text ID character bitmaps (5x7 font) are overlayed for 7 lines, repeating for odd/even fields (14 lines).
- At line 156, the system is held at reset, repeating the last line 16 times until the next frame, awaiting another vertical interval.
-
A0–A6 (7 bits):
Selects the first 140 lines of the pattern.- Driven by a cascaded 4-bit binary ripple counter (
74HC393, IC7) clocked at 5 MHz for the pixel clock.
- Driven by a cascaded 4-bit binary ripple counter (
-
A7–A10 (4 bits):
Selects 14 lines dedicated to the white ID overlay text.- Managed by a binary up counter (
CD4520, IC5:B).
- Managed by a binary up counter (
-
A11–A12 (2 bits):
Pattern selector via the front panel pattern selection toggle switch.
Summary:
- 7 bits = 2K pattern block addressing, effectively supporting 4 patterns.
- The 4th pattern is not used unless the center-off toggle switch is replaced with a 4-position selector.
| Address Range | A12 | A11 | Description | Pattern |
|---|---|---|---|---|
| 0x0000–0x07FF | 0 | 0 | Pattern 0 (2K) | Pattern (color bars) |
| 0x0800–0x0FFF | 0 | 1 | Pattern 1 (2K) | Pattern (split filed red bars) |
| 0x1000–0x17FF | 1 | 0 | Pattern 2 (2K) | Pattern (pulse & bar) |
| 0x1800–0x1FFF | 1 | 1 | Pattern 3 (2K) | Patter (color black) |
Pattern Layout per block of 2K:
| Address Range | Pattern cycle | Function |
|---|---|---|
| Pattern 1 | ||
| 0x0000-0x008F | Initial color bars (8 bars each of 16 pixels) | Iterates over 1 x 128 pixels |
| 0x0080-0x077F | Main pattern with text ID over color bars | odd/even field, 14 lines x 128 pixels |
| 0x0780-0x07FF | Last pattern color bars (8 bars each of 16 pixels) | Iterates over 1 x 128 pixels |
| Pattern 2 | ||
| 0x0800-0x087F | Initial color bar (8 bars each of 16 pixels) | Iterates over 1 x 128 pixels |
| 0x0880-0x0F7F | Main pattern with text ID over color bars | odd/even field, 14 lines x 128 pixels |
| 0x0F80-0x0FFF | Last pattern split bars (128 of Red pixels) | Iterates over 1 x 128 pixels |
| Pattern 3 | ||
| 0x1000-0x107F | Initial color bar (8 bars each of 16 pixels) | Iterates over 1 x 128 pixels |
| 0x1080-0x177F | Main pattern with text ID over color bars | odd/even field, 14 lines x 128 pixels |
| 0x1780-0x17FF | Last pattern pulse & bar ( pulse 1 pixel, bar 8 pixels) | Iterates over 1 x 128 pixels |
| Pattern 4 | ||
| 0x1800-0x187F | Initial color black (128 pixels of black) | Iterates over 1 x 128 pixels |
| 0x1080-0x177F | Main pattern no text 14 x 128 pixels of balck | odd/even field, 14 lines x 128 pixels |
| 0x1780-0x17FF | Last pattern color black (128 of Black pixels) | Iterates over 1 x 128 pixels |
| Data line | channel |
|---|---|
| D0 | GREEN |
| D1 | RED |
| D2 | BLUE |
| D3 | WHITE |
Note - Although the combination of D0 AND D1 AND D2 make white, D3 is used as an independant white signal to cancel out effects of 100% white. The white is added to the red and blue matrix in the U-V modulator.
Each of color outputs are latched by a 74HC273 (IC8) to provide a stable digital RGBW to the luminace and U-V matrix.
The toggle switch connected to A11 and A12 allows selection between the two active pattern blocks:
Position 1: A11=0, A12=1 → Selects Pattern 1 (0x0800–0x0FFF)
Position 2: A11=0, A12=0 → Selects Pattern 2 (0x0000–0x07FF)
Position 3: A11=1, A12=0 → Selects Pattern 3 (0x1000–0x17FF)
Position 4: A11=1, A12=1 → Selects Pattern 4 (0x1000–0x17FF) (Not usable without modification of the front toggle switch as noted.)
Here's the pictures of the 4 patterns with the 1st picture showing the original id overlay before generation of new patterns.
Original ID |
Color Bars |
Split Field Red Bars |
Pulse & Bar |