MC68HC08AZ16 Datasheet, PDF (427/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Appendix A: Related Devices
External address
bus - A[15:0]
The external address bus are the output address signals from the EBI
module. They provide addressing information to the external devices. In
Low Noise mode the values on these lines remain at the last driven state
between external accesses.
Chip-selects - CS1, The chip-selects are output control signals from the EBI module. They
CS0
enable external devices at their programmed addresses.
External data bus -
DB[7:0]
The external data bus are three-state bidirectional data signals to the
EBI module. These signals provide the data path between the MCU and
all external devices. In Low Noise mode the values on these lines
remain at the last driven state between external accesses.
External read - REB
The external read is an output control signal from the EBI module. When
REB is asserted, a read cycle starts and data is transferred from an
external device to the internal data bus. This signal is asserted only for
external accesses, or when the IRV bit is set.
External write -
WEB
The external write is an output control signal to the EBI module. When
WEB is asserted, a write cycle starts and data is transferred to an
external device from the internal data bus. This signal is asserted only
for external accesses or when the IRV bit is set.
WAIT state clock -
WSCLK
The WAIT state clock is used to insert the correct number of WAIT states
into each bus cycle when the ‘external WAIT states’ operating mode is
selected for CS0.
Functional
description
MC68HC08AZ32
426
The user has two optional chip-select lines to define areas within the 64K
byte address range to be occupied by external devices. The range of
each address chip-select region can be modified by software. The
software option provides the user with a choice of regions as shown in
Figure 5.
SCS1 is intended for program space as it always includes the vector
space. CS0 may be used for any purpose and is in effect equivalent to
CS1. Extending CS0 address space below $1000 allows the user to
place external devices (e.g. I/O) in unused address locations below
Appendix A: Related Devices
14-appA
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