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XC2200 Derivatives
System Units (Vol. 1 of 2)
The External Bus Controller EBC
User’s Manual
9-1
V2.1, 2008-08
EBC_X8, V1.0d1
9
The External Bus Controller EBC
All external memory accesses are performed by a particular on-chip External Bus
Controller (EBC). It can be programmed either to Single Chip Mode when no external
memory is required at all, or dynamically (depending on the selected address range,
belonging to a chip-select signal) to one of four different external memory access modes,
which are as follows:
•
1 … 24-bit Addresses, 16-bit Data, Demultiplexed
•
1 … 24-bit Addresses, 16-bit Data, Multiplexed
•
1 … 24-bit Addresses, 8-bit Data, Multiplexed
•
1 … 24-bit Addresses, 8-bit Data, Demultiplexed
Note: The following description refers to the general EBC feature set. In the 100-pin
package, some features are not available, see
. In the 64-pin package,
no external bus interface is available.
In the multiplexed bus modes, the intra-segment address outputs (A15 … A0) and data
input/outputs are overlaid on 16 port pins. The higher segment address outputs
(A23 … A16) are mapped to separate port pins. In the demultiplexed bus modes,
address outputs and data input/outputs are not overlaid but mapped to the port pins
separately. For applications which do not use all address lines for external devices, the
external address space can be restricted by enabling only the required address lines. Up
to 5 external CS signals can be generated in order to save external glue logic. Memories
or peripherals with variable access time are supported via a particular ‘Ready’ function.
A HOLD/HLDA protocol is available for bus arbitration.
The XC2200 External Bus Controller (EBC) allows access to external
peripherals/memories and to internal LXBus modules. The LXBus is an internal
representation of the ExtBus and it controls accesses to integrated peripherals and
modules in the same way as accesses to external components.
The function of the EBC is controlled via a set of configuration registers. The basic and
general behaviour is programmed via the mode-selection registers EBCMOD0 and
EBCMOD1.
Similar to the supported external bus chip-select channels, LXBus modules are selected
by a specific chip select signal (both access types are handled as ‘external’ accesses by
the EBC).
The Function CONtrol register for CSx (FCONCSx) register specifies the external
bus/LXBus cycles in terms of address (multiplexed/demultiplexed), data (16-bit/8-bit),
READY control, and chip-select enable. The timing of the bus access is controlled by the
Timing CONfiguration registers for CSx (TCONCSx), which specify the timing of the bus
cycle with the lengths of the different access phases. All these parameters are used for
accesses within a specific address area that is defined via the corresponding ADDRess
SELect register ADDRSELx.