Cirrus Logic CRYSTAL LAN CS890, Техническое справочное руководство

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AN83REV1 17
CS8900 Technical Reference Manual
The last few bytes of the EEPROM are
used to store information about the hard-
ware configuration and software require-
ments.
Please refer to the section 3.5 and 3.6 of the
CS8900 data sheet for information about
programming the EEPROM. Please refer
to the Section 3.0 of this document for in-
formation about EEPROM internal word
assignment.
2.2.2.5 Socket For Optional Boot PROM
A socket is provided at location U6 for the
optional Boot PROM . This Boot PROM
is required in systems that require remote
boot capability, for example diskless work
stations. The 74LS245 data buffer at U7 is
provided for the Boot PROM (See Figure
2.2.4). Inside the CS8900 there are regis-
ters that hold the Boot PROM base address
(PacketPage base + 030h) and the Boot
PROM address mask (PacketPage base +
034h). A 20 bit address loaded at the Boot
PROM base address register indicates the
starting location in host memory where the
Boot PROM is mapped. The Boot PROM
address mask indicates the size of the Boot
PROM . The lower 12 bits of the mask are
ignored and should be 000h. This limits
the 434 Boot PROM size to increments of
4K bytes. The CS8900 will not generate an
address decode for the Boot PROM until
the Boot PROM base address register and
the mask register are loaded. For example,
say a 16K Boot PROM is used and it is to
be located starting at address 0D0000h.
Before this Boot PROM is accessed, load
the following registers with the values
shown in Table 2.2.1.
Register Word
Offset
PacketPage Base +
Hex value Description
30h 0000h Boot PROM Base address - low word
32h 000Dh Boot PROM Base address - high word
34h C000h Boot PROM address mask - low word
36h 000Fh Boot PROM address mask - high word
Table 2.2.1. BootPROM Descriptions Stored in CS8900 PacketPage
The address mask that will be used by the
CS8900 is 0FC000h. The CS8900 will
compare SA[19:14] with the value 0D0h.
Whenever there is a match, it will assert the
signal CSOUT* to generate an address de- code for the Boot PROM . In the reference
design, the same signal is also used to en-
able the data buffer, 74LS245, at location
U7.