4Kx42 Theory of Operation

This page describes how specific components operate on BrightSign 4K players.

Power Supply

There are several voltage levels present in BrightSign 4K players.

Reset

BrightSign 4K 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.

BCM7444/7252 CPU

The 4K242 and 4K1042 utilize a BCM7252 CPU, while the 4K1142 utilizes a BCM7444 CPU. 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 CPU will boot from the NAND flash.

Built-in Flash

The boot code in the BCM7252/BCM7444 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

The 4K1142 contains six banks of DDR SDRAM (two 4GB banks and four 2GB banks), while the 4K242 and 4K1042 each 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 1067MHz, with a data rate of 2133MT/s.

Serial Port

The 4K1042 and 4K1142 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.

Audio Outputs

BrightSign 4K 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 4K 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 4K series 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 10/100/1000 Base-T Ethernet is implemented on 4K players by directly interfacing with the BCM7252/BCM7444. The player has on-board Ethernet magnetics and termination for the RJ-45 cable.

USB 2.0/3.0

The USB 2.0/3.0 high-speed host controller is implemented internally on the BCM7252/BCM7444 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.