NanoBoard 3000 - Video Output

The NanoBoard 3000 provides a standard SVGA (Super Video Graphics Array) interface, for connection to any SVGA-compatible monitor. Analog RGB video output (24-bit/80MHz) is made through a DB15F connector.

Video output connector.

 
The analog R, G and B signals – required for output to a connected monitor – are obtained by passing the 24-bit digital RGB video signal (RGB, 8-bits parallel) through a THS8134 Video DAC device (from Texas Instruments). Powered by 5V (analog) and 3.3V (digital) supplies, this device contains three 8-bit, 80MSPS video DACs. These are used to convert the VGA_RED[7..0], VGA_GREEN[7..0] and VGA_BLUE[7..0] digital input signals, generated by a VGA Controller in the FPGA design programmed into the User FPGA.

The device is set to operate as three 8-bit (RGB) ports by tying the M1 and M2 pins Low. Additional sync and blanking controls have been disabled, with the respective inputs tied High or Low as required to render these controls inactive.

Clocking for the device is courtesy of the VGA_CLK signal from the FPGA design. This is typically sourced from the external system clock signal to the design (CLK_I), which is also used as the pixel clock for the in-design VGA Controller. Data for all three input ports (R, G, B) is clocked in at each rising edge of VGA_CLK and all three DACs operate at this clock speed.

Each DAC uses an internally generated reference voltage of 1.35V (nominal).

The analog R, G and B outputs, along with VGA_VSYNC and VGA HSYNC signals from the FPGA design's VGA Controller, are wired to the DB15 connector, for output to a connected monitor. All five of these signal lines are protected against transient voltages (caused for example by ESD) through use of a TVS diode array device – an SMF05C, from Semtech.

Table 1 summarizes the pinout of the DB15 connector, in terms of standard SVGA interface, and which pins are actually connected on the NanoBoard.

For each color, the 8-bit digital signal can be converted into 256 distinct analog levels. These levels specify the intensity of each of the three primary colors to use when displaying the pixel on a connected monitor's screen. By driving each output into a 75Ω load prior to the connector, standard video output levels are achieved, ranging from 0V (total darkness) to 0.7V (maximum brightness). With each analog input being one of 256 possible levels, the monitor can display each pixel on the screen with one of 16777216 color permutations.

Location on Board

The DB15 connector – labeled 'SVGA VIDEO - 24BIT/80MHZ' and designated J18 – is located along the top edge on the solder side of the board. Looking from the rear, it can be found between the host USB port (J10) and the MIDI ouput port (J22).

Video output connector (as seen from the rear of the
board).

The THS8134 device (designated U21) and the SMF05C device (designated U20) are also located on the solder side of the board, below the DB15 connector.

Video DAC (U21) and TVS diode array (U20).

Schematic Reference

The video output circuitry can be found on the following sheets of the motherboard schematics:

• Sheet 51 (VGA_OUT.SchDoc, entitled VGA Output)

• Sheet 52 (VIDEO_DAC_THS8134B.SchDoc, entitled Video DAC)

• Sheet 53 (CON_VGA_DB15.SchDoc, entitled Video Out Connector)

Design Interface Component

Table 2 summarizes the available design interface component that can be placed from the FPGA NB3000 Port-Plugin.IntLib for access to, and communications with, the video output device (THS8134).

Further Device Information

For more information on the THS8134 device, refer to the datasheet (ths8134.pdf) available at www.ti.com.

For more information on the SMF05C device, refer to the datasheet (SMF05C.pdf) available at www.semtech.com.