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MC9S12H256 Device User Guide — V01.18

Section 4 Modes of Operation

4.1 Overview

Eight possible modes determine the operating configuration of the MC9S12H256. Each mode has an

associated default memory map and external bus configuration.

Three low power modes exist for the device.

4.2 Modes of Operation

The operating mode out of reset is determined by the states of the MODC, MODB, and MODA pins during

reset (Table 4-1). The MODC, MODB, and MODA bits in the MODE register show the current operating

mode and provide limited mode switching during operation. The states of the MODC, MODB, and MODA

pins are latched into these bits on the rising edge of the reset signal.

There are two basic types of operating modes:

1. Normal modes: Some registers and bits are protected against accidental changes.

2. Special modes: Allow greater access to protected control registers and bits for special purposes such

as testing.

A system development and debug feature, background debug mode (BDM), is available in all modes. In

special single-chip mode, BDM is active immediately after reset.

Some aspects of Port E are not mode dependent. Bit 1 of Port E is a general purpose input or the IRQ

interrupt input. IRQ can be enabled by bits in the CPU’s condition codes register but it is inhibited at reset

so this pin is initially configured as a simple input with a pull-up. Bit 0 of Port E is a general purpose input

or the XIRQ interrupt input. XIRQ can be enabled by bits in the CPU’s condition codes register but it is

inhibited at reset so this pin is initially configured as a simple input with a pull-up. The ESTR bit in the

EBICTL register is set to one by reset in any user mode. This assures that the reset vector can be fetched

Table 4-1 Mode Selection

MODC

MODB

MODA

Mode Description

000

Special Single Chip, BDM allowed and ACTIVE. BDM is allowed in all

other modes but a serial command is required to make BDM active.

Emulation Expanded Narrow, BDM allowed

Special Test (Expanded Wide) (Motorola Use Only), BDM allowed

Emulation Expanded Wide, BDM allowed

Normal Single Chip, BDM allowed

Normal Expanded Narrow, BDM allowed

110

Peripheral (Motorola Use Only); BDM allowed but bus operations

would cause bus conﬂicts (must not be used)

Normal Expanded Wide, BDM allowed

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