SAF-C164SM Infineon Technologies, SAF-C164SM Datasheet - Page 175

• Manufacturer Part Number: SAF-C164SM
• Description: 16-Bit CMOS Microcontroller
• Manufacturer: Infineon Technologies

Switching between Bus Modes
The EBC allows switching between the 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, an 8-bit or 16-bit data bus, or predefined waitstates.
Changes to the external bus characteristics can be initiated in two different ways:
Switching between predefined address windows automatically selects the bus mode
associated with the respective window. Predefined address windows allow use of
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.
PORT1 will output the intra-segment address when any of the BUSCON registers
selects a demultiplexed bus mode, even if the current bus cycle uses a multiplexed bus
mode. This allows to have an external address decoder connected to PORT1 only, while
using it for all kinds of bus cycles.
The usage of the BUSCON/ADDRSEL registers is controlled via the issued addresses.
When an access (code fetch or data) is initiated, the respective generated physical
address defines whether the access made internally uses one of the address windows
defined by ADDRSEL4 … 1 or it uses the default configuration in BUSCON0. After
initializing the active registers, they are selected and evaluated automatically by
interpreting the physical address. No additional switching or selecting is necessary
during run time, except when more than the four address windows plus the default are
to be used.
Reprogramming the BUSCON and/or ADDRSEL registers allows either changing the
bus mode for a given address window or changing the size of an address window using
a certain bus mode. Reprogramming allows a great number of different address windows
to be used (more than the BUSCONs available) at the expense of the overhead for
changing the registers and keeping appropriate tables.
Note: Be careful when changing the configuration for an address area that currently
Switching from demultiplexed to multiplexed bus mode represents a special case.
The bus cycle is started by activating ALE and driving the address to PORT1 as usual,
if another BUSCON register selects a demultiplexed bus. However, in the multiplexed
User’s Manual
supplies the instruction stream. Due to the internal pipelining, the first instruction
fetch that will use the new configuration depends on the instructions prior to the
configuration change. Special care is required when changing bits like BUSACT,
in order not to cut the instruction stream inadvertently.
Only change the other configuration bits after checking that the respective
application can cope with the intended modification(s).
It is recommended to change ADDRSEL registers only while the respective
BUSACT bit in the associated BUSCON register is cleared.
9-6
External Bus Interface
C164CM/C164SM
Derivatives
V1.0, 2002-02