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11

5. PHYSICAL INTERFACE

5.1

Power Supply

The transient response of the regulator is important. If the power rails of the module are

supplied from an external voltage source, the transient response of any regulator used

should be 20µs or less.

5.2

RF Interface

The module integrates a balun filter. The user can connect a 50ohms antenna directly to the

RF port. The module integrates PCB antenna.

5.3

Serial Interfaces

5.3.1

USB

There is a full speed (12M bits/s) USB interface for communicating with other

compatible digital devices. The module acts as a USB peripheral, responding to request

from a master host controller, such as a PC.

The module features an internal USB pull-up resistor. This pulls the USB_DP pin weakly

high when module is ready to enumerate. It signals to the USB master that it is a full

speed (12Mbit/s) USB device. The USB internal pull-up is implemented as a current

source, and is compliant with section7.1.5 of the USB specification v1.2. The internal

pull-up pulls USB_DP high to at least 2.8V when loaded

with

a

15k

±5%

pull-down resistor (in

the hub/host) when

VDD

=3.1V. This presents a The

venin resistance to the host of at least 900 . Alternatively, an external 1.5k

pull-up

resistor can be placed between a PIO line and DP on the USB cable.