UM0581

Design details

Doc ID 14961 Rev 1

13/26

either an 8 or 16-bit data path. Here the device is configured in 16-bit MUX mode to connect

with the external hard disk.

The STR91xFA provides a USB device controller that implements both the OSI physical and

data link layers (complicated) for direct bus connection by an external USB host on pins

USBDP and USBPN.

3.4

Reset circuit

The reset signal of STR912FAW44 is an active low signal. The reset source includes

●

Power-on reset from STM6718TW

●

Reset button (SW1)

The STM6718TW supervisors are a family of low voltage/low supply current processor

supervisors, designed to monitor two (or three) system power supply voltages. The purpose

of this IC is to monitor the core voltage (1.8 V) and IO peripheral voltage (3.3 V). The reset

button (SW1) is provided to manually reset the board.

3.5

Clock source

The 25 MHz crystal is connected between the X1 and X2 pin of the microcontroller to

provide the clock to the device.

3.6

USB

The STR912FAW44 parallel interface to hard disk demonstration board supports USB 2.0

compliant full speed communication via a USB type-B connector (J11). The USBLC6-2SC6

is a monolithic application specific device dedicated to ESD protection of high speed

interfaces such as USB2.0, ethernet links and video lines. Here this device is connected

between the USB connector and microcontroller.

3.7

LED indicators

●

SYS-HEALTH-CHK LED (D4): This LED indicates the board is properly powered up as

well as the correct initialization of the connected hard disk.

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RD-LED (D5): This LED blinks when a read operation is performed on the hard disk.

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WR-LED (D6): This LED blinks when a write operation is performed on the hard disk.