21285-AB Originated Transactions - Intel Corporation

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21285-AB

Manufacturer Part Number
21285-AB
Description
Microprocessor, 21285 Core Logic For SA-110 Microprocessor
Manufacturer
Intel Corporation
Datasheet

Specifications of 21285-AB

Case
BGA
Dc
99+/00+
Transactions
All 21285 transactions occur between the SA-110, PCI, SDRAM, ROM, and X-Bus.
Figure 3-1
shows the three FIFOs used in performing the various transactions.
Outbound FIFO (256 bytes)
— SA-110 write addresses and data for PCI
— SA-110 read addresses for PCI
— DMA write addresses and data for PCI
— DMA read addresses for PCI
Inbound FIFO (256 bytes)
— PCI write addresses and data for SDRAM and ROM
— PCI read addresses for SDRAM and ROM
— DMA write data for SDRAM
— SA-110 read data from PCI
PCI Read FIFO (128 bytes)
— PCI read data from SDRAM and ROM
3.1
SA-110 Originated Transactions
The following sections describe SA-110 originated bus transactions. These transactions are
classified by their address spaces (refer to
The 21285 controls the SA-110 clock, MCLK, by stretching the high time to stall the SA-110
during bus cycles (indicated by assertion of nMREQ by SA-110). The number of cycles that
MCLK stays high may be different for each address space and depends upon other 21285 activity
at the time nMREQ asserts.
3.1.1
CSR Write
The SA-110 write data is written to the selected CSR (the CSR with offset equal to SA-110 address
A[10:2]). The SA-110 is normally stalled for three cycles, but can be stalled longer. If a
nonexistent CSR is selected within the CSR address range, the write data is discarded (no error
action is taken).
The CSR address space is listed in Tables 7-2, 7-3, and 7-4.
3.1.2
CSR Read
The selected CSR (the CSR with offset equal to SA-110 address A[10:2]) read data is driven onto
D[31:0]. If a nonexistent CSR is selected within the CSR address range, zeros are read (no error
action is taken). The SA-110 normally stalls for three cycles.
21285 Core Logic for SA-110 Datasheet
Table
5-1).
3
3-1

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