MC68HC711D3CFNE2 Datasheet, PDF (35/124 Pages) Freescale Semiconductor, Inc – Power Saving STOP and WAIT Modes

Freescale Semiconductor, Inc.
SECTION 4
OPERATING MODES AND ON-CHIP MEMORY
This section contains information about the modes that define MC68HC11D3 operat-
ing conditions, and about the on-chip memory that allows the MCU to be configured
for various applications.
4.1 Operating Modes
The values of the mode select inputs MODB and MODA during reset determine the
operating mode. Single chip and expanded multiplexed are the normal modes. With
single-chip mode only on-board memory is available. Expanded multiplexed mode,
however, allows access to external memory. Each of these two normal modes is
paired with a special mode. Bootstrap, a variation of the single-chip mode, is a special
mode that executes a bootloader program in an internal bootstrap ROM. Test is a spe-
cial mode that allows privileged access to internal resources.
4.1.1 Single-Chip Mode
In single-chip mode, ports B and C are available for general-purpose parallel I/O. In
expanded multiplexed mode the MCU can access a 64 Kbyte address space. The total
address space includes the same on-chip memory addresses used for single-chip
mode plus external memory and peripheral devices.
4.1.2 Expanded Multiplexed Mode
Expanded memory access is achieved by providing multiplexed external data and ad-
dress buses on two of the M68HC11 ports; therefore only 18 pins are needed for an
8-bit data bus, a 16-bit address bus and two bus control lines. Port B is designated for
ADDR[15:8], while port C is multiplexed ADDR[7:0]/DATA[7:0]. The address, R/W,
and AS signals are active and valid for all bus cycles including accesses to internal
memory locations. Refer to Figure 4-1, which illustrates a recommended method of
demultiplexing low order addresses from data at port C.
OPERATING MODES AND ON-CHIP MEMORY
TECHNICAL DATA
4-1
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