NS7520B-1-I46 Digi International, NS7520B-1-I46 Datasheet - Page 164

• Manufacturer Part Number: NS7520B-1-I46
• Description: IC ARM MICROPROCESSOR 177BGA
• Manufacturer: Digi International
• Series: NET+ARM®r

Specifications of NS7520B-1-I46

• Applications: Network Processor
• Core Processor: ARM7
• Program Memory Type: External Program Memory
• Controller Series: -
• Ram Size: External
• Interface: EBI/EMI, Ethernet, DMA, SPI, UART
• Number Of I /o: 16
• Voltage - Supply: 1.4 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 177-LFBGA
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Receive buffer descriptor selection
1 5 2
E t h e r n e t f r o n t - e n d ( E F E )
The MAC forwards good Ethernet packets through address filtering. Packets can be
filtered based on station address, broadcast, and select multicast packets. Those
packets that pass through address filtering are moved into system memory.
When an Ethernet frame is received, the Ethernet receiver DMA channel searches the
four buffer descriptors — starting with A and continuing with B, C, and D, as
necessary — for an appropriately sized buffer. The search stops when the DMA
channel finds an available buffer that is large enough to hold the entire Ethernet
receive frame. The search also stops when the DMA channel finds a Control register
whose Channel Enable (CE) bit is zero.
Figure 22 shows receiver buffer size selection.
Figure 22: Receive buffer size selection
descriptor
smallest
buffer
DMA
" A"
list
N S 7 5 2 0 H a r d w a r e R e f e r e n c e , R e v G 9 / 2 0 0 7
descriptor
buffer
DMA
" B"
list
RX DMA channel
2048-byte
receive
FIFO
descriptor
buffer
DMA
" C"
list
descriptor
largest
buffer
DMA
" D"
list