Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement - Manual (Page 187)

High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
187
USING WAKE-UP FRAMES
As discussed in the DS80C400 data sheet, the Ethernet controller can be placed into a low-power sleep mode such that it can be awak-
ened by a user-programmable network wake-up frame and/or magic packet. The magic packet must conform to a specific predefined
frame format, while the user-programmable network wake-up frame gives the application flexibility in defining the wake-up frame.
MAGIC PACKET MODE
When put into the magic packet mode, the power-management block constantly monitors each frame addressed to the device for a
specific magic packet pattern. Only packets that pass the current destination address filter are checked against the magic packet
requirement. Each frame received is checked for an FFFF_FFFF_FFFFh pattern after the destination and source address fields. This
pattern must be followed by 16 repetitions of the physical MAC address without any breaks or interruptions. In case of a break in the
16 repetitions of the MAC physical address, the FFFF_FFFF_FFFFh pattern is scanned for again in the frame. The 16 repetitions can be
anywhere in the frame, but they must be preceded by the synchronization stream.
For example, if the MAC address of a device were 00-11-22-33-44-55, then the MAC would scan for the following frame data sequence:
[DestinationAddress][ SourceAddress] ................FFFF FFFF FFFF 0011 2233 4455 0011 2233 4455
0011 2233 4455 0011 2233 4455 0011 2233 4455 0011 2233 4455 0011 2233 4455 0011 2233 4455
0011 2233 4455 0011 2233 4455 0011 2233 4455 0011 2233 4455 0011 2233 4455 0011 2233 4455
0011 2233 4455 0011 2233 4455 ...............CRC
NETWORK WAKE-UP FRAME
Before putting the MAC into sleep mode, the host provides a list of sample frames and the corresponding byte masks to the wake-up
frame filter register in the power-management block through the wake-up frame filter (28h) register. In order to know which bytes of each
receive frame should be included in the CRC-16 calculation, the power-management block uses a programmable byte mask and a pro-
grammable pattern offset for each of the supported filters. In order to load the wake-up frame filter register, the host has to perform
eight writes to the wake-up frame filter register. The wake-up frame filter structure is illustrated in the DS80C400 data sheet. The first
write loads the filter 0 byte mask, the second write loads the filter 1 byte mask and so on. The fifth write loads the filter command nib-
ble for each frame filter. Bit 3 of each filter [0,1,2,3] command nibble, or wake source (WS), is used in conjunction with the global uni-
cast (GU) bit of the wake-up events control and status (2Ch) CSR register to define what type of frames are compared to the wake-up
frame filters. Bit 0 of each filter [0,1,2,3] command nibble enables the associated wake-up frame filter. Table 22-4 summarizes the pos-
sible GU, WS bit combinations. Note that a broadcast frame is always compared versus the enabled wake-up frame filters. One option
to easily allow any broadcast frame to serve as a network wake-up frame is to disable all filter byte mask bits (= 00_00_00_00h) and
designate that the required filter CRC-16 be 0000h (default CRC-16 value). Steps 1 through 8 show an example sequence for pro-
gramming wake-up filter 0. Figure 22-14 shows the resultant filter.
Table 22-4. Network Wake-Up Frame Patterns
GU, WS NETWORK WAKE-UP FRAME CRITERIA (IF FRAME FILTER ENABLED)
00 Unicast, pass destination address filter, pass wake-up frame filter
01 Multicast, pass destination address filter, pass wake-up frame filter
10 Unicast, pass wake-up frame filter
11 Multicast, pass wake-up frame filter
xx Broadcast, pass wake-up frame filter
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