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nRF24AP2-USB Product Specification

This section outlines the enumeration process, user configurable USB parameters, and message

exchanges that take place on the nRF24AP2-USB host interface.

5.3.1

Physical USB connection

The physical connection between nRF24AP2-USB and the host must follow the USB standard v2.0 (for

instance, use USB approved connectors) in order for your nRF24AP2-USB based application to go

through USB compliance testing.

5.3.2

USB enumeration

The USB enumeration process is handled by the nRF24AP2-USB. During the enumeration the host reads

out the USB descriptors and strings to determine which device has been connected to the bus. After the

host has received the parameters it will then assign the device an address and allowing it to transfer data

on the bus.

A typical enumeration process consists of the following steps:

1.

The host detects a new device on the bus via the pull up resistor on D+.

2.

The host issues a reset to place the nRF24AP2-USB to the default state. This will enable the

device to respond to the default address zero requests.

3.

The host requests the Device Descriptor on address 0.

4.

The host issues another bus reset.

5.

The host issues a set address command, placing the nRF24AP2-USB in an addressed state.

6.

The host requests the Device Descriptor again.

7.

The host requests the Configuration, Interface and Endpoint Descriptors.

8.

The host requests the String Descriptors.

After the enumeration process the nRF24AP2-USB can transfer ANT messages on the bus. A complete

summary of ANT messages supported are listed in Table 4. on page 20.

5.3.3

USB descriptors

The nRF24AP2-USB has a set of USB descriptors which describe to the host information about manufac-

turer, product, USB version, the number of endpoints and their types.

Figure 12. Organization of USB descriptors

Device Descriptor

Configuration Descriptor

Interface Descriptor

Endpoint

Descriptor 1 IN

Endpoint

Descriptor 1 OUT