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Write cycles: The command signal is now deactivated. If a subsequent external bus cycle is
required, the EBC places the respective address on the address bus. The data remain valid
on the bus until the next external bus cycle is started.
9.2.3
Switching between bus modes
The EBC can be used to switch between different bus modes dynamically, i.e. subsequent
external bus cycles may be executed in different ways. Certain address areas may use
multiplexed or demultiplexed buses or use READY control or predefined waitstates.
A change of the external bus characteristics can be initiated in two different ways:
Reprogramming the BUSCON and/or ADDRSEL registers allows to either change the
bus mode for a given address window, or change the size of an address window that uses a
certain bus mode. Reprogramming allows to use a great number of different address
windows (more than BUSCONs are available) on the expense of the overhead for changing
the registers and keeping appropriate tables.
Switching between predefined address windows automatically selects the bus mode that
is associated with the respective window. Predefined address windows allow to use different
bus modes without any overhead, but restrict their number to the number of BUSCONs.
However, as BUSCON0 controls all address areas, which are not covered by the other
BUSCONs, this allows to have gaps between these windows, which use the bus mode of
BUSCON0.
Figure 53 Demultiplexed bus cycle
