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PEB 20321
PEF 20321
Local Bus Interface (LBI)
Data Sheet
156
2001-02-14
The address port LA(15:0) drives the address used last.
LRD/LWR remain inactive (High).
6.2.6
In high performance systems it may be efficient to share external resources like memory
banks or peripheral devices among more than one bus controller. The LBI
’
s EBC block
supports this approach with the possibility to arbitrate the access to its external bus, i.e.
to the external devices.
This bus arbitration allows an external master to request the EBC
’
s bus via the LHOLD
input. The EBC acknowledges this request via the LHLDA output and will float its bus
lines in this case. The new master may now access the peripheral devices or memory
banks via the same interface lines as the EBC. During this time the MUNICH32X can
continue executing internal processes, as long as it does not need access to the external
bus.
When the EBC needs access to its external bus while it is occupied by another bus
master, the bus is requested via the LBREQ output.
The external bus arbitration is enabled by setting bit HLDEN in the LBI Configuration
register to
‘
1
’
. This bit may be cleared during the execution of program sequences, where
the external resources are required, but cannot be shared with other bus masters. In this
case the EBC will not answer to LHOLD requests from other external masters.
Note: The pins LHOLD, LHLDA and LBREQ maintain their functionality (bus arbitration)
even after the arbitration function has been switched off by clearing HLDEN.
All three pins are used for bus arbitration after bit HLDEN was set once.
External Bus Arbitration
Entering the Hold State
Access to the EBC
’
s external bus is requested by driving its LHOLD input low. After
synchronizing this signal the EBC will complete a current external bus cycle (if any is
active), release the external bus and grant access to it by driving the LHLDA output low.
During hold state the EBC manages the external bus interface as follows:
Address and data bus(es) float to tri-state.
Command lines become inputs (LRD, LWR, LBHE).
Should the MUNICH32X require access to its external bus during hold mode, it activates
its bus request output LBREQ to notify the arbitration circuitry. LHOLD is activated only
during hold mode. It will be inactive during normal operation.