XDx32 Theory of Operation

This page describes how specific components operate on the XD232, XD1032, and XD1132.

Power Supply

There are seven voltage levels present in the player: 12V, 5V, 3.3V, 2.5V, 1.8V, 1.5V, and 1V.

Reset

BrightSign XDx32 players have a Low Voltage Reset circuit. This circuit will hold the RESET_L signal low until a valid 3.3V power source is present.

BCM7434 CPU

BrightSign XDx32 players utilize a BCM7434 Multimedia CPU. This CPU runs on 3.3V, 2.5V, and 1V and runs from a 27MHz oscillator. The CPU is reset by the RESET_L signal from the low voltage reset circuit going into the RESET_IN pin on the CPU. When the RESET_IN pin goes from low to high, the BCM7434 will boot from the NAND flash.

Built-in Flash

The boot code in the BCM7434 instructs it to continue the boot process by reading additional code from the onboard NAND flash, which can be updated in the field, either from a SDHC/SDXC flash card or a USB mass-storage device. Part of the NAND flash is also used to hold non-volatile parameters. The contents of the boot flash are copied into the SDRAM. The CPU then jumps to the boot code.

SDRAM

BrightSign XDx32 players contain four banks of DDR SDRAM (two 2GB banks and two 4GB banks). When the CPU boots, it will copy the code from the NAND flash device into the SDRAM and then execute the code from the SDRAM. The SDRAM runs at a clock rate of 800MHz, with a data rate of 1600MHz.

Serial Port

The XD1032 and XD1132 have a built in UART that communicates with the RS-232 level shifter. The MAX232 uses a capacitive voltage switcher to create valid RS-232 voltage levels for the transmit pin.

Video Encoder and Filter

The BCM7421 streams decoded video using a single-data rate clock. It also streams the same video out of the on-board DACs.

Audio Outputs

BrightSign XDx32 players each have a single high quality audio DAC device, which takes in digital audio signals from the CPU in an I2S audio format. The AUD_LRCIN is the framing signal for the audio and runs at the frame rate of the audio source (usually either 44.1KHz or 48KHz). The AUD_BITCLK signal is typically 32 times higher than the AUD_LRCIN.

The audio output is fed through an amplifier and sent directly to the audio output jack. It can drive a 32Ω load with a 2V RMS signal.

On-Board LEDs

There are eight on-board LEDs that indicate the following:

On-Board Switch

The on-board switch is connected to the GPIO12, which is pulled low when the service (SVC) button is pressed. Conversely, a pull-up on the button normally sets the GPIO12 to be pulled high.

Reset Switch/GPIO Button

The on-board switch is connected to the reset circuit. Pressing down the reset button will cause the GPIO07 to go low. Holding the reset button low for approximately 10 seconds will cause a hard reset. When the board goes into reset mode, the power LED will be dark until the reset button is released.

SDHC/SDXC and MicroSD Slots

The XDx32 series has one SDHC/SDXC and one internal MicroSD card slot, both capable of transferring a 25 Mbit/sec video stream, one 5.1 AC3 stream (pass-through), and three stereo PCM tracks simultaneously. There is no inherent limit on the storage capacity of SD cards used for XDx32 players.

NAND Flash

BrightSign players have a built-in NAND flash. All the code for the player is stored on the NAND flash. It may also be possible to store some content on the NAND flash, which is connected directly to the CPU.

Ethernet

The 10/100 Base-T Ethernet is implemented on XDx32 players by directly interfacing with the BCM7434. The player has on-board Ethernet magnetics and termination for the RJ-45 cable.

USB

The USB 2.0 high-speed host controller is implemented internally in the BCM7434 SOC. The board utilizes over-current protected switches that can be used to turn the power to USB devices on or off or to detect over-current situations.