Theory Of Operation; Power Supply; Reset; Pnx8935 Cpu - Roku Compact Hardware Manual

BrightSign Compact

Theory of operation

Power Supply

The Brightsign Compact has a five voltages present. These are 5V, 3.3V, 2.5V, 1.8Vand 1.2V. 5V
comes in from the power connector and is used directly for USB, the video filter chip.. 3.3V is created
from 5V by a Semtech SC196 switching regulator. Similar regulators are used to create 2.5V for the DDR
SDRAM, 1.8V for the HDMI chip, and 1.2V for the PNX8935 core voltage.

Reset

The Brightsign Compact has a Low Voltage Reset circuit made up of a ADM809SAKS. This circuit will
hold the RESET_L signal low until a valid 3.3V power is present.

PNX8935 CPU

The Brightsign Compact has a Philips PNX8935 Multimedia CPU in it. This CPU runs on 3.3V, 2.5V,
and 1.2V. The PNX8935 runs from a 27MHz oscillator. The PNX8935 is reset by the signal RESET_L
from the low voltage reset circuit going into the RESET_IN pin on the PNX8935. When the RESET_IN
pin goes from low to high, then the PNX8935 will boot from NAND flash.

Built in Flash

The HD2000 contains 3 flash devices. The boot code in the PNX8935 instructs the PNX8935 to continue
the boot process by reading additional code from the on board NAND flash. This flash can be updated in
the field, either from on the flash slots or USB mass storage. Part of the NAND flash is also used to hold
non-volatile parameters. The contents of the boot flash is copied into the SDRAM, then the PNX8935
jumps to the boot code. There is also a serial settings flash that can be used to contain non-volatile
settings. The last flash is the Ethernet flash that is used to configure the Ethernet PHY chip.

SDRAM

The HD2000 contains four DDR SDRAM devices. When the PNX8935 boots, it will copy the code from
the NAND flash device into SDRAM, and then execute the code from SDRAM. The SDRAM runs at
clock rate 200MHz, with data rate 400MHz.

Serial Port

The Brightsign Compact has a built in UART that that communicates with the RS232 level shifter. The
MAX232 creates valid RS232 voltage levels for the transmit pin by using a capacitive voltage switcher.

Video Encoder and Filter

The PNX8935 streams decoded video out of the QVCP5L digital port using single data rate clock, and it
also streams the same video out of the on board DACs. Analog video comes out of the PNX8935 and is
connected to the FMS6203 video filter chip. This chip has a programmable cutoff frequency of either
8MHz, 16MHz or 32MHz, or no filter. Since the video filter has a low impedance output, we can drive
both VGA and COMPONENT 75Ohm terminated cables at the same time with no degradation (with the
This information applies to a product under development. Its characteristics and specifications are subject to change without notice. Roku assumes no
obligation regarding future manufacturing unless otherwise agreed to in writing. www.rokulabs.com © Roku 2008