SC2200 NSC [National Semiconductor], SC2200 Datasheet - Page 158

• Manufacturer Part Number: SC2200
• Description: Thin Client On a Chip
• Manufacturer: NSC [National Semiconductor]

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Core Logic Module
5.2.5.3
The Core Logic module performs all of the required data
steering from SD[7:0] to SD[15:0] during normal 8-bit ISA
cycles, as well as during DMA and ISA master cycles. It
handles data transfers between the 32-bit PCI data bus
and the ISA bus. 8/16-bit devices can reside on the ISA
bus. Various PC-compatible I/O registers, DMA controller
registers, interrupt controller registers, and counter/timer
registers lie on the on-chip I/O data bus. Either the PCI bus
master or the DMA controllers can become the bus owner.
When the PCI bus master is the bus owner, the Core Logic
module data steering logic provides data conversion nec-
essary for 8/16/32-bit transfers to and from 8/16-bit devices
on either the Sub-ISA bus or the 8-bit registers on the on-
chip I/O data bus. When PCI data bus drivers of the Core
Logic module are in TRI-STATE, data transfers between
the PCI bus master and PCI bus devices are handled
directly via the PCI data bus.
When the DMA requestor is the bus owner, the Core Logic
module allows 8/16-bit data transfer between the Sub-ISA
bus and the PCI data bus.
Fast-PCI
ISA
1 - GX1 transaction
2 - IDE bus master - starts and completes
3 - End of ISA cycle
Sub-ISA Bus Data Steering
RD#, IOR#
FRAME#
TRDY#
STOP#
IRDY#
REQ#
GNT#
BALE
Figure 5-3. PCI to ISA Cycles with Delayed Transaction Enabled
(Continued)
1
1
1
158
5.2.5.4
In normal operation, the Core Logic module inserts a delay
between back-to-back ISA I/O cycles that originate on the
PCI bus. The default delay is four ISACLK cycles. Thus, the
second of consecutive I/O cycles is held in the ISA bus
controller until this delay count has expired. The delay is
measured between the rising edge of IOR#/IOW# and the
falling edge of BALE. This delay can be adjusted to a
greater delay through the ISA I/O Recovery Control register
(F0 Index 51h).
Note:
2
This delay is not inserted for a 16-bit Sub-ISA I/O
access that is split into two 8-bit I/O accesses.
I/O Recovery Delays
1
3
Revision 3.0