WY-50 Video Replacement
Notes
This is a project to interface with the video connector for the WY-50 terminal.
The video connection is via a 12 pin connector. Pin numbering matches the schematic. Nominal colours are from the schematic, actual colours are from the connector. Signal is the signal name. Note that pin 1 as labelled on the connector is pin 12.
| Pin | Nominal Colour | Actual Colour | Signal |
|---|---|---|---|
| 1 | White | White | VIDEO |
| 2 | Black | Black | GND |
| 3 | Orange | Orange | !DIM |
| 4 | Yellow | Yellow | HSYNC |
| 5 | Green | Green | VSYNC |
| 6 | Blue | Blue | +12V |
| 7 | Grey | Grey | -12V |
| 8 | Red | Red | +5V |
| 9 | Black | Black | GND |
| 10 | Black | Brown | GND |
| 11 | Purple | Purple | -23V |
| 12 | Red | White | +5V |
When the connector is unplugged, only pin 8 has +5V on it. When connected the other volatages are present suggesting that the other voltages are generated on the main board or are not generated without some main board work. Glancing at the schematics, it does not appear that we care too much; we can just use the +5V rail and send the VIDEO/HSYNC/VSYNC signals.
The following trace shows the VSYNC signal (top) and HSYNC (bottom):
Signals appear to be ~3V peak-to-peak. VSYNC has a frequency of 60Hz, HSYNC has a frequency of 22.7kHz. VSYNC pulse width is 133µs. HSYNC pulse width is 16µs.
The following trace shows the HSYNC signal (top) and VIDEO signal (bottom) for the horizontal line on the display along with the cursor on the line below.
HSYNC frequency as measured by the hardware counter is 22.5kHz. The visible line width is 34µs. The end of the visible area is associated with the +ve going HSYNC edge.
The VIDEO signal itself indirectly drives the electron gun and so may be regarded as an analogue signal:
If we leave !DIM disconnected we can drive intensity through the VIDEO signal alone.
Timings
Inferred timings from the above:
| Parameter | Value | Note |
|---|---|---|
| Total vertical lines | 375 | = 22500Hz / 60Hz |
| Visible vertical lines | 360(?) | Based on manual's claim of up to 44 lines (+1 status) at 8 lines/char |
| Character clock | 2.3529MHz(?) | Based on 80 chars/visible line |
| Frame rate | 60Hz | |
| VSYNC pulse width | 133µs | Appears to be 3 line periods |
| HSYNC pulse width | 16.6µs | |
| Line duration | 44.4µs | |
| Visible line duration | 34.0µs |