User`s manual

Am186™CC Microcontroller Router Reference Design User’s Manual
2-23
USB PC Interface
NOTE: See sheet 12 in the schematics for the USB PC interface circuitry.
The Am186CC microcontroller router reference design provides a full-speed
(12 Mbit/s) peripheral USB port that enables the reference design to be used as a
self-powered USB peripheral.
You can configure the reference design to use the Am186CC microcontroller full-
speed (12 Mbit/s) USB peripheral controller’s integrated USB transceiver. Using
the internal USB transceiver enables the USB differential signaling (USBD+ and
USBD–) to directly connect to the USB connector and to a USB host or hub through
a standard USB full-speed cable.
When the USB port is active, the Am186CC microcontroller’s PIO8 signal is driven
Low, which illuminates LED CR7 (at location F-9).
The Am186CC microcontroller can be used only as a self-powered USB peripheral
because of the power requirements needed in typical applications. Because of the
USB electrical requirements of self-powered USB peripherals, there is a small
amount of glue logic needed to meet the USB specifications. The attach/detach
scenarios addressed with this logic are described in the following paragraphs.
Attach
1. The Am186CC microcontroller polls PIO42 for a logic High level to detect an
active host/hub upstream connection (USBVCC is on). In the case where an
active USB host/hub is connected to the Am186CC microcontroller router
reference design USB port and power is not applied to the reference design,
Q2 (at location J-2) isolates the USBVCC from the reference design to prevent
damage to the Am186CC microcontroller.
2. The Am186CC microcontroller drives PIO43 High to enable Q1 (at location
J-2), which pulls R67 up to 3.3 V. This pulls up the USBD+ signal to indicate
to the host that a full-speed USB device is present.
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