Freescale Semiconductor MCF5480 - Manual (Page 539)

Functional Description
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 19-55
its secondary bus as a Type 0 configuration access, decoding the device number to select one of the IDSEL
lines. If the bus number is not equal to its secondary bus, but is within the range of buses that are
subordinate to the bridge, the bridge claims and passes that access through as a Type 1 access.
Figure 19-51. PCI-to-PCI Bridge Determining Match to Secondary or Subordinate Bus
19.4.1.5.4 Address Decoding
For positive address decoding, an address hits when the address on the address bus matches an assigned
address range. Multiple devices on the same PCI bus may use positive address decoding, though there
cannot be any overlap in the assigned address ranges. The MCF548x only implements positive address
decoding.
For subtractive address decoding, an address hits when the address on the address bus does not match any
address range for any of the PCI devices on the bus. Only one device on a PCI bus may use subtractive
address decoding, and its use is optional.
19.4.2 Initiator Arbitration
There are three possible internal initiator sources: comm bus transmit, comm bus receive, or the XL bus
(from the internal system arbiter). Custom interface logic arbitrates and provides multiplex selection
control for these sources to the PCI controller. Figure 19-52 illustrates the arbitration block connection.
PCI
Bridge
PCI
Bridge
Secondary
Bus
Subordinate
Bus
Primary
Bus
MCF548x
.
Device 0.0
.
Device 1.0
Device 0.1
Device 1.1
Device 0.2
Device 1.2
Device 2.2
Device 3.2
Responds
to Type 0
Responds
to Type 0