W89C940 Datasheet, PDF (14/61 Pages) Winbond – ELANC-PCI (TWISTED-PAIR ETHER-LAN CONTROLLER WITH PCI INTERFACE)

W89C940
BOOT PROM ACCESS FUNCTION
Boot PROM Operation
For diskless applications, the system requires an on-board boot device. The ELANC-PCI allows the system to
use an on-board BOOT PROM as the boot device.
The BOOT PROM is essentially a byte-read device. ELANC-PCI will fetch a byte from the BOOT PROM and
drive the AD bus of the PCI Interface. If the system do a word read command, the ELANC-PCI will invoke two
byte read operation with consecutive address and drove the second byte on another byte of the PCI interface.
For double word command, the ELANC-PCI will deassert the TRDY# until four read operation with consecutive
address to the BOOT PROM is completed and then the four bytes of data will be drove onto the 32 bits data bus
of PCI.
W89C940 can support the EPROM and Flash memory with 220nsec access time with the size up to 256KB. In
order to support 64KB,128KB and 256KB size with 15-bit address bus, W89C940 use MSA14 to latch the high
address bits MSA[17:14] from MSA[13:10]. The structure for address latch is shown as following.
W89C940
MSA[9:0]
MSA[13:10]
EPROM
MSA[17:14]
MSA14/L
74LS373
14