Datasheet

Microchip MRF24W Getting Started Guide for MRF24WB0MA/B, MRF24WG0MA/B for MLA v5
DS52108A-page 38 Preliminary  2013 Microchip Technology Inc.
4.5.3 MAC Address
In the system there are three sources for the MAC address:
• Built-in MAC address on the MRF24WB0MA/B or MRF24WG0MA/B WiFi
®
mod-
ule that is preprogrammed from the factory with the MRF24WB0MA/B or
MRF24WG0MA/B Wi-Fi
®
OUI
• Programmed code image
• Value that is stored in the EEPROM
At run-time, a data structure is created in RAM, which stores the valid MAC address
(amongst other information) to be used for that session. The code will check if a valid
data structure is located in the EEPROM. If the valid data structure exists in EEPROM,
then those values will be used, overriding what is programmed inside the chip and/or
programmed in the code at compile-time.
If no data structure exists in the EEPROM, then the value that is stored in the
\configs\TCPIP MRF24W.h file will be used. If the value in the source code is
00:04:A3:00:00:00, then it indicates to the program that the value that has been
preprogrammed in the MRF24WB0MA/B or MRF24WG0MA/B Wi-Fi
®
module should
be used. Otherwise, the value that is placed into the MY_DEFAULT_MAC_BYTEx will be
used. Additionally, if no valid data structure exists in the EEPROM, the new value will
be programmed and stored to the EEPROM for the future use.
EEPROM has the highest priority. Therefore, if a value for the MAC address is
programmed to the EEPROM, no other value can override it. To change the values,
EEPROM must be erased. Refer to the instructions specified in 5.3 “Erasing
EEPROM”.
4.5.4 Channel Configuration
802.11b and 802.11g divide the 2.4 GHz spectrum into 14 channels, from channel 1
through channel 14. The bandwidth of each channel is 20 MHz which means that chan-
nels may overlap. The commonly used non overlapping channels and social channels
are channels 1, 6 and 11.
The RF channel that is used can be configured at compile-time. The following two inter-
related options control channels data transmission:
• Regulatory domain, as specified by MY_DEFAULT_DOMAIN. Different domains
have different channel offerings, hence it must match with the intended country
and channel
• Channel scan list (MY_DEFAULT_CHANNEL_LIST), which is an array of chan-
nels that will be scanned for RF activity.
As illustrated in Figure 4-7, the domain is set to FCC and there are 11 total channels in
the scan list (1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11).
Note: If more channels to scan, it takes longer time to connect.