MC68HC711D3_05 Datasheet, PDF (21/138 Pages) Freescale Semiconductor, Inc – Microcontrollers

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
register (HPRIO) on the rising edge of reset. The normal operating modes are the single-chip and
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.
Table 2-1. Mode Selection
RESET
1
1
1
1
0
MODA
0
1
0
1
0
MODB
Mode Selected
1 Normal — single chip
1 Normal — expanded multiplexed
0 Special — bootstrap (BOOT)
0 Special — test
0 Reserved
SMOD
0
0
1
1
X
MDA
0
1
0
1
X
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.
MC68HC711D3 Data Sheet, Rev. 2.1
Freescale Semiconductor
21