Siemens SIMATIC RI 45 PIII Series, Manual

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RI 45 PIII, Manual
C79000-G7076-C817-01
The Pentium II CPU has a memory address area of 64 Gbytes; 4 Gbytes of
this can be used. The CPU has a 64-bit wide data bus, 33 address lines, and 8
bus enable lines (BE0...BE7) which code the non-existent byte address lines
A0, A1 and A2. The CPU address bus is mapped on the PCI address bus via
the PAC (system controller). Excluded from this are the memory addresses
from 0000 0000h to 0009 FFFFh (640 Kbytes) and from 0010 0000h to 2FFF
FFFFh (768MByte)).
The ISA-Bridge PIIX (PCI ISA IDE Xcellerator) maps the ISA address bus
exactly once on the PCI address bus. The ISA address bus for 8-bit modules
covers the address area from A0 to A19, corresponding to the CPU addresses
0000 0000h to 000F FFFFh (1 Mbyte). For 16-bit ISA modules, the address
bus is extended by the address lines A20...A23 and therefore addresses from
0000 0000h to 00FF FFFFh (16 Mbytes). The differentiation between the 1
Mbyte and 16 Mbyte ISA address areas is achieved using special memory
read/write signals which are only activated if the address lines A20, A21,
A22 and A23 have a level of logical “0”. If the CPU addresses areas which
are occupied by the main memory, no ISA bus control signals are generated.
This means that an ISA bus module is not addressed in these memory areas.
On the contrary, an ISA bus master cannot reach addresses above 16 Mbytes.
In order to achieve a larger address area for dual-port RAM extensions than
the memory address area between 640 Kbytes and 1 Mbytes, special decoder
hardware is provided on the Pentium programming device basic module:
The CPU address area from FFF0 0000h to FFFD FFFFh (1024k - 128k
BOIS = 896 KB) is mapped into the ISA address area 00F0 0000h to
00FD FFFFh and is always addressed in the CPU address area. Decoding
of the address lines A24 to A31 missing on the ISA bus is achieved using
special hardware on the basic module.
The CPU address area from 00F0 0000 to 00FF FFFF is mapped into the
ISA address area from 00F0 0000 to 00FF FFFF (16 Mbyte memory
window). This setting can be switched on and off in the setup.
2.10 DMA Channels
DMA Channel Data Transfer Description
0 8/16 bit Sound*
1 8/16 bit Sound*
2 8/16 bit Floppy
3 8/16 bit
4 Cascading of DMA controller
5 16 bit Free
6 16 bit Free
7 16 bit Free
* Can be switched off by deactivating the sound card
Memory Decoding
Function
Motherboard