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Internal Patterns

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4.3 Internal Patterns

In addition to the externally provided sequences through the 24-bit RGB interface of the DLPC300, the

DLP LightCrafter offers the ability to pre-load patterns into the DLPC300’ s memory (mDDR) to achieve

faster frame rates. Once the patterns are pre-loaded, the FPGA manages the bit planes stored in the

mDDR. The mDDR accommodates four 608 × 684 images of 24-bit RGB data or 96 bit-planes (24 bit-

planes × 4 images). The 96 bit-plane buffer is arranged in a circular buffer style, meaning that the last bit

plane addition to the buffer replaces the oldest stored bit plane.

The oldest set of bit planes in the bit-plane buffer is displayed. Thus, the displayed patterns will lag by

16.66 ms at 60 Hz frame rate while the circular buffer is filled. After the initial 16.66-ms delay, there is no

additional delay for subsequent patterns since the circular buffer is filled.

With the FPGA, the pattern frame rate can be calculated with the following equation:

Pattern Rate = (1/Pattern Exposure Period) + (Bit Plane Load Time) + (Buffer Rotate Overhead)

where

• Typical bit plane load time = 230 µs

• Typical buffer rotate overhead = 135 µs (2)

Table 4-2 shows the maximum pattern rate that can be achieved by using a single FPGA’s internal buffer

in continuous mode.

Table 4-2. Maximum Internal Pattern Rate

MAXIMUM NUMBER OF MAXIMUM PATTERN RATE

COLOR MODE

PATTERNS

1-bit per pixel 96 4000 Hz

2-bit per pixel 48 1600 Hz

3-bit per pixel 32 480 Hz

4-bit per pixel 24 360 Hz

Monochrome

5-bit per pixel 16 240 Hz

6-bit per pixel 16 240 Hz

7-bit per pixel 12 180 Hz

8-bit per pixel 12 120 Hz

These locally stored patterns have a pre-defined exposure time that is detailed in Table 4-3. Note that the

exposure time decrements by 500 µs from the maximum exposure time. Thus, the minimum might not be

a step size decrease from the second to last minimum exposure time.

Table 4-3. Internal Pattern Exposure Time

MAXIMUM EXPOSURE MINIMUM EXPOSURE STEP SIZE DECREASE

BIT DEPTH

TIME (µs) TIME (µs) (µs)

8-bit 20,000 8,333 500

7-bit 20,000 4,500 500

6-bit 20,000 2,500 500

5-bit 20,000 2,000 500

4-bit 20,000 1,600 500

3-bit 20,000 1,470 500

2-bit 20,000 666 500

1-bit 100,000 250 500

Pattern Sequences DLPU006C–January 2012–Revised December 2013

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