Tech FAQ
Tech FAQ
Once a channel is opened you can change:
• Channel Frequency
• Network Key
• Device #, Device Type, Transmission Type
• Channel Period
• Transmit power
• Search Timeout , Low Priority Search Timeout
• Inclusion/Exclusion list entries and configuration
Network:
Assign Channel:
Channel ID:
Channel Frequency:
Channel Period:
Search Timeout:
Transmit Power:
To configure a single ANT channel you need to:
• Set the network key (0x46)
• Assign the channel (0x42)
• Set channel ID (0x51)
• Set RF frequency (0x45)
• Set channel period (0x43)
• Set transmit power (0x60)
• Set search timeout (0x44) - Slave only
• And finally open the channel (0x4B)
To minimize the number of commands you can use the default values (defined in next question below), leaving only the following commands required:
• Assign the channel (0x42)
• Set channel ID (0x51)
• Open the channel (0x4B)
See section 5.3 of the ANT Message Protocol and Usage document for more information on establishing a channel and Section 9 for command details.
For a private or a public network, the device type, device number and transmission type can be user defined. As a suggested implementation, the device type is a number that represents the class (or type) of the master device. Other devices of the same class should also be recognised with the same device type. Device types must be set on master devices (slaves may wildcard this value).
The device number is a unique number representing a specific master device. Typically this may be correlated to the serial number of the device, or randomly generated if serial numbers are not supported. Device numbers must be set on master devices (slaves may wildcard this value).
An easy way to understand device type and number is to consider yourself as an ANT device. Your device type might be “human”, and your device number could be represented by your name.
The transmission type is a number that represents the different transmission characteristics of a device, and must be specified on master devices (slaves may wildcard this value). This is determined by the manufacturer or pre-defined in an ANT+ network. The two least significant bits of the transmission type are used to indicate the presence, and size, of a shared address field at the beginning of the data payload, and the third least significant bit is used to indicate the presence of a Global Data Identification Byte (such as ANT+ page numbers). The most significant nibble may be used to extend the device number.
Yes. There are no dependencies between channel parameters – each channel can be a master or a slave, and can have different channel periods, frequencies, networks (up to a maximum of 3 networks per device), etc.
A decimated channel is a channel that recieives data at a reduced channel period, which is a factor of the transmitting device's channel period.
For example if a master channel is transmitting at 4Hz, a slave could be set up to receive at 2Hz, or 1Hz instead of the normal 4Hz. In this case the slave device would receive every second, or every fourth, message. The slave is then said to be receiving data at a decimated rate.
The device number is a 2 byte value that is part of the channel ID. The purpose of the device number is to identify an individual device. As the device number is a 2 byte value it can be used to distinguish between 2^16 devices.
The device number can be extended by using the top nibble of the transmission type (also part of the channel ID) as the top nibble of the "extended device number". Therefore the extended device number can be used to distinguish between 2^20 devices.
If the device number is 0xF5E4 and the Transmission Type is 0x35, then the extended device number will be 0x3F5E4.
Shared channels allow a master to connect to several slaves on one channel, and to send messages to each slave based on the slave's shared address.
The shared address can be either 1 or 2 bytes in size (indicated by the transmission type) and should be unique for each slave. The shared address 0x00 (or 0x0000) is reserved and is used by the master to send messages to all slaves at once.
To set the shared address on each slave, configure the channel as a shared slave (channel type 0x02, appropriate transmission type etc) and then send a broadcast message from the slave with the shared address field set to the desired address for that slave. This broadcast message sets the slaves shared address, so in future it will only receive messages from the master that contain its shared address or 0. Sending another broadcast message from the slave with a different shared address would change the slave's shared address to the new value (although it is unlikely you would want to do this).
Please refer to the "Implementation using Shared Channels" example in the ANT Message Protocol and Usage document for details. As a more advanced option you can also refer to Application Note 07 Auto Shared Channel Master Example. These are available on the documents tab of the downloads page.
