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Software Developer’s Manual 391
Appendix (82540EP/EM and 82545GM/EM Differences)
Appendix (82540EP/EM and 82545GM/EM Differences)B
B.1 Introduction
This section describes the differences between the 82546GB/EB, the 82540EP/EM and the
82545GM/EM. All three of these Ethernet controllers come from the same family so their register
sets are essentially the same. The sections that follow describe the differences between the
82546GB/EB and the 82540EP/EM or 82545GM/EM, and resulting register differences and
developer impact.
B.2 82540EP/EM Differences
Below are the differences between the 82540EP/EM and the 82546GM/EM:
• Serial FLASH interface. The 82540EP/EM does not support a parallel FLASH interface.
• No TBI/internal SerDes interface. The 82540EP/EM provides internal GMII / MII
interfaces only
• Single-port functionality. The dual-port functionality of the 82546GB/EB is not included.
• 32-bit PCI support only. The 82540EP/EM does not support 64-bit PCI or PCI-X.
• Internal SerDes. The 82540EP/EM does not support internal SerDes.
The impact to registers and the developer are outlined in the following sections.
B.2.1 Serial FLASH Interface
The 82540EP/EM provides an external interface to a serial Flash or Boot EPROM device.
Hardware implements a serial command set compatible with the Atmel AT25-series devices in the
512 Kb (64 KB) thru 1024 Kb (128 KB) sizes. The size of the FLASH used with the 82540EP/EM
should be encoded into bits in EEPROM to configure the amount of address space required when
mapped. All accesses to this device are controlled by hardware and are accessible to software as
normal PCI reads or writes to the FLASH memory mapping range. The FLASH and Expansion
ROM BARs are reconfigured based on these EEPROM settings.
Note: The 82540EP/EM serial FLASH controller supports reads from programmed FLASH devices, and
writes to erased FLASH devices. Chip and sector-erase commands are not supported. It is
recommended that FLASH devices be socketed to enable removal for re-programming if
necessary.