DS-88

# DS-88 "Digisector" NTSC Frame Grabber

The DS-88 Digisector is an early video frame grabber designed for the IBM PC by a company called The Micro Works. They also made an Apple II version called teh DS-65 Digisector, and an S-100 version called the DS-80.

It uses a discrete successive approximate ADC to capture the video frame one pixel at a time. Since the SAR ADC is relatively slow, it's not able to digitize the entire frame at once. Instead, it uses a set of vertical and horizontal counters to trigger the
ADC to capture a pixel at a particular, consistent place in the frame. You can see this point by connecting a video monitor
to the output RCA jack, where the current pixel will be highlighted.

There are three adjusment knobs on the edge of the card. The one marked W adjust the width of the captured image. B adjusts the brightness, and C adjusts the contrast.

## Registers

The registers are mapped to an IO port set by the switch bank. The card comes with the address set at 0x330. The address bits controlled by each switch are marked on the card (A2-A9).

There are four registers total; two of them are read only, and the other two are write-only.

| Address | Read/Write | Function |
|---------|------------|----------|
| 0       | Read       | ADC results |
| 1       | Read       | Status register |
| 0       | Write      | Horizontal pixel location |
| 1       | Write      | Vertical pixel location |

The status register bit assignments are as follows:

| Bit | Function |
|-----|----------|
| 0   | Unused |
| 1   | Unused |
| 2   | Horizontal counter most significant bit |
| 3   | Vertical counter most significant bit |
| 4   | Conversion in progress |
| 5   | 0=hsync in progress |
| 6   | 0=vsync in progress |
| 7   | Conversion result ready |

See the files in the asm subdirectory for programming examples.