Datasheet

MC68HC711D3 Data Sheet, Rev. 2.1

Freescale Semiconductor 21

Chapter 2

Operating Modes and Memory

2.1 Introduction

This section contains information about:

• The modes that define MC68HC711D3 operating conditions

• The on-chip memory that allows the microcontroller unit (MCU) to be configured for various

applications

• The 4-Kbytes of programmable read-only memory (PROM)

2.2 Operating Modes

The MC68HC711D3 uses two dedicated pins, MODA and MODB, to select one of two normal operating

modes or one of two special operating modes. A value reflecting the microcontroller unit (MCU) status or

mode selected is latched on bits SMOD and MDA of the highest priority I-bit interrupt and miscellaneous

expanded-multiplexed modes. The special operating modes are the bootstrap and test modes. Table 2-1

shows mode selection according to the values encoded on the MODA and MODB pins, and the value

latched in the SMOD and MDA bits.

2.2.1 Single-Chip Mode

In single-chip mode, the MCU functions as a self-contained microcontroller and has no external address

or data bus. The 4-Kbyte erasable programmable read-only memory (EPROM) would contain all program

code and is located at $F000–$FFFF. This mode provides maximum use of the pins for on-chip peripheral

functions, and all the address and data activity occurs within the MCU.

2.2.2 Expanded Multiplexed Mode

In the expanded-multiplexed mode, the MCU can address up to 64 Kbytes of address space. High-order

address bits are output on the port B pins. Low-order address bits and the bidirectional data bus are

multiplexed on port C. The AS pin provides the control output used in demultiplexing the low-order

address. The R/W

pin is used to control the direction of data transfer on the port C bus.

Table 2-1. Mode Selection

RESET MODA MODB Mode Selected SMOD MDA

1 0 1 Normal — single chip 0 0

1 1 1 Normal — expanded multiplexed 0 1

1 0 0 Special — bootstrap (BOOT) 1 0

1 1 0 Special — test 1 1

0 0 0 Reserved X X