CS5920 datasheet(87/160 Pages) AMCC

87 / 160 page

S5920 – PCI Product

Revision 1.01 – November 28, 2005

AMCC Confidential and Proprietary

DS1596

Data Book

wire serial arbitration. It assumes that it is the only

master on the bus.

Communications with the serial memory involve sev-

eral clock transitions. A start event signals the

beginning of a transaction and is immediately followed

by an address transfer. Each address/data transfer

consists of 8 bits of information followed by a 1-bit

acknowledgment. When the exchange is complete, a

stop event is issued. Figure 2 shows the unique rela-

tionship defining both a start and stop event. Figure 3

shows the required timing for address/data with

respect to the serial clock.

For random accesses, the sequence involves one

clock to define the start of the sequence, eight clocks

to send the slave address and read/write command,

followed by a one-clock acknowledge, and so on. Fig-

ure 4 shows the sequence for a random write access

requiring 29 serial clock transitions. At the clock speed

of the S5920, this corresponds to one byte of data

transferred approximately every 0.25 milliseconds.

Read accesses can be either random or sequential.

During boot-up, all accesses from address 40h to 7Fh

are sequential. As a result, it is important the nvRAM

used supports the nvRAM sequential read accesses

as indicated in Figure 6. Figure 5 shows the sequence

for a random byte read.

To initialize the S5920 controller’s PCI Configuration

Registers, the smallest serial device necessary is a

128 x 8 organization. Although the S5920 controller

only requires 64 bytes, these configuration bytes must

begin at the 64-byte address offset (40h through 7Fh).

This offset constraint permits the configuration image

to be shared with a memory containing expansion

BIOS code and the necessary preamble to identify an

expansion BIOS. The largest serial device which can

be used is 2 Kbytes.

Table 49. Valid External Boot Memory Contents

Address

Data

Notes

0040h-0041h

not FFFFh

This is the location that the S5920 will load a customized vendor ID. (FFFFh is an

illegal vendor ID.)

0050h

82h - registers to I/O

81h - memory space

80h - memory below

1 Mbytes

This is the least significant byte of the region which initializes the S5920 configura-

tion register BADR0. A value of 81h assigns the 32 DWORD locations of the PCI

operations registers into I/O space, a value of 80h defines memory space, and a

value of 82h defines memory space below 1 Mbytes.

0051h

FFh

Required

0052h

E8h

Required

0053h

10h

Required

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