Intel PCI User Manual

391

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 

 and the 82540EP/EM or 82545GM/EM, and resulting register differences and 

developer impact.

Below are the differences between the 82540EP/EM and the 82546GM/EM:

•

 The 82540EP/EM does not support a parallel FLASH interface.

•

 The 82540EP/EM provides internal GMII / MII 

interfaces only

•

 The dual-port functionality of the 82546GB/EB is not included.

•

 The 82540EP/EM does not support 64-bit PCI or PCI-X.

•

 The 82540EP/EM does not support internal SerDes.

The impact to registers and the developer are outlined in the following sections.

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. 

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.