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XC2200 Derivatives
System Units (Vol. 1 of 2)
Architectural Overview
User’s Manual
2-14
V2.1, 2008-08
ArchitectureX22, V1.1
External Bus Interface
To meet the needs of designs where more memory is required than is provided on chip,
up to 12 Mbytes of external RAM/ROM/Flash or peripherals can be connected to the
XC2200 microcontroller via its external bus interface.
All of the 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, or to an external bus mode with the following possible selections
1)
:
• Address Bus Width with a range of 0 … 24-bit
• Data Bus Width 8-bit or 16-bit
• Bus Operation Multiplexed or Demultiplexed
In the demultiplexed bus modes, addresses are output on Port 0 and Port 1 and data is
input/output on Port 10 and Port 2. In the multiplexed bus modes both addresses and
data use Port 10 and Port 2 for input/output. The high order address (segment) lines use
Port 2. The number of active segment address lines is selectable, restricting the external
address space to 8 Mbytes … 64 Kbytes. This is required when interface lines are
assigned to Port 2.
For up to five address areas the bus mode (multiplexed/demultiplexed), the data bus
width (8-bit/16-bit) and even the length of a bus cycle (waitstates, signal delays) can be
selected independently. This allows access to a variety of memory and peripheral
components directly and with maximum efficiency.
Access to very slow memories or modules with varying access times is supported via a
particular ‘Ready’ function. The active level of the control input signal is selectable.
A HOLD/HLDA protocol is available for bus arbitration and allows the sharing of external
resources with other bus masters.
The external bus timing is related to the rising edge of the reference clock output
CLKOUT. The external bus protocol is compatible with that of the standard C166 Family.
For applications which require less than 64 Kbytes of address space, a non-segmented
memory model can be selected, where all locations can be addressed by 16 bits. Thus,
the upper Port 2 is not needed as an output for the upper address bits (Axx … A16), as
is the case when using the segmented memory model.
The EBC also controls accesses to resources connected to the
on-chip LXBus
. The
LXBus is an internal representation of the external bus and allows accessing integrated
peripherals and modules in the same way as external components.
The MultiCAN module and the USIC modules are connected to and accessed via the
LXBus.
1)
Bus modes are switched dynamically if several address windows with different mode settings are used.