Intel Embedded Intel486 Hardware Reference Manual page 48

EMBEDDED Intel486™ PROCESSOR HARDWARE REFERENCE MANUAL
64-Bit Interunit Transfer Bus
Base/
Barrel Segmentation
Index
Shifter
Bus
Descriptor
Register 32
Registers
File
Limit and
ALU
Attribute PLA
Micro-
Instruction
Control &
Protection
Test Unit
Control
ROM
Figure 3-3. Ultra-Low Power Intel486™ SX and Ultra-Low Power Intel486 GX Processors
Signals from the external 32-bit processor bus reach the internal units through the bus interface
unit. On the internal side, the bus interface unit and cache unit pass addresses bi-directionally
through a 32-bit bus. Data is passed from the cache to the bus interface unit on a 32-bit data bus.
The closely coupled cache and instruction prefetch units simultaneously receive instruction
prefetches from the bus interface unit over a shared 32-bit data bus, which the cache also uses to
receive operands and other types of data. Instructions in the cache are accessible to the instruction
prefetch unit, which contains a 32-byte queue of instructions waiting to be executed.
The on-chip cache is 16 Kbytes for the IntelDX4 processor and 8 Kbytes for all other members
of the Intel486 processor family. It is 4-way set associative and follows a write-through policy.
The Write-Back Enhanced IntelDX4 processor can be set to use an on-chip write-back cache pol-
3-4
32-Bit Data Bus
32-Bit Data Bus
Linear Address 32
PCD
PWT
2
Paging
Unit
Unit
20
Physical
Address
Translation
Lookaside
Buffer
Displacement Bus
32
Code
Stream
Instruction
24
Decode
Decoded
Instruction
Path
Block Diagram
Core
Clock
Clock
Control
Bus Interface
Cache Unit
Address
32
Drivers
Write Buffers
8 Kbyte
32
4 x 32
Cache
Data Bus
32
Transceivers
Bus Control
Prefetcher
Request
Sequencer
32-Byte Code
Burst Bus
Queue
Control
Bus Size
2x16 Bytes
Control (on
ULP486 SX
only)
Cache
Control
Parity
Generation
and Control
Boundary
Scan
Control
CLK
A31-A2
BE3#- BE0#
D31-D0 on ULP486™ SX
D15-D0 on ULP486™ GX
ADS# W/R# D/C# M/IO#
PCD PWT RDY# LOCK#
PLOCK# BOFF# A20M#
BREQ HOLD HLDA
RESET SRESET INTR
NMI SMI# SMIACT#
FERR# IGNNE#
STPCLK#
BRDY# BLAST#
BS16# BS8# (not present
on ULP486 GX)
KEN# FLUSH#
AHOLD EADS#
DP3-DP0 PCHK# on
ULP486 SX
DP1-DP0 PCHK# on
ULP486 GX
TCK TMS
TDI TD0
A5440-01