NXP Semiconductors LPC24XX UM10237 - Manual (Page 215)

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User manual Rev. 04 — 26 August 2009 215 of 792
NXP Semiconductors
UM10237
Chapter 11: LPC24XX Ethernet
A receive filter block is used to identify received frames that are not addressed to this
Ethernet station, so that they can be discarded. The Rx filters include a perfect address
filter and a hash filter.
Wake-on-LAN power management support makes it possible to wake the system up from
a power-down state -a state in which some of the clocks are switched off -when wake-up
frames are received over the LAN. Wake-up frames are recognized by the receive filtering
modules or by a Magic Frame detection technology. System wake-up occurs by triggering
an interrupt.
An interrupt logic block raises and masks interrupts and keeps track of the cause of
interrupts. The interrupt block sends an interrupt request signal to the host system.
Interrupts can be enabled, cleared and set by software.
Support for IEEE 802.3/clause 31 flow control is implemented in the flow control block.
Receive flow control frames are automatically handled by the MAC. Transmit flow control
frames can be initiated by software. In half duplex mode, the flow control module will
generate back pressure by sending out continuous preamble only, interrupted by pauses
to prevent the jabber limit from being exceeded.
The Ethernet block has both a standard IEEE 802.3/clause 22 Media Independent
Interface (MII) bus and a Reduced Media Independent Interface (RMII) to connect to an
external Ethernet PHY chip. MII or RMII mode can be selected by the RMII bit in the
Command register. The standard nibble-wide MII interface allows a low speed data
connection to the PHY chip: 2.5 MHz at 10 Mbps or 25 MHz at 100 Mbps. The RMII
interface allows a low pin count double clock data connection to the PHY. Registers in the
PHY chip are accessed via the AHB interface through the serial management connection
of the MII bus (MIIM) operating at 2.5 MHz.
5.2 Example PHY Devices
Some examples of compatible PHY devices are shown in Table 11–182 .
5.3 DMA engine functions
The Ethernet block is designed to provide optimized performance via DMA hardware
acceleration. Independent scatter/gather DMA engines connected to the AHB bus off-load
many data transfers from the ARM7 CPU.
Table 182. Example PHY Devices
Manufacturer Part Number(s)
Broadcom BCM5221
ICS ICS1893
Intel LXT971A
LSI Logic L80223, L80225, L80227
Micrel KS8721
National DP83847, DP83846, DP83843
SMSC LAN83C185