MCMC68HC05L16 Freescale Semiconductor, Inc, MCMC68HC05L16 Datasheet - Page 135

• Manufacturer Part Number: MCMC68HC05L16
• Description: M68hc05 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

A.7 Modes of Operation
The MC68HC705L16 has the following operating modes: single-chip mode (SCM) and bootstrap mode.
Single-chip mode, also called user mode, allows maximum use of pins for on-chip peripheral functions.
The bootstrap mode is provided for EPROM programming, dumping EPROM contents, and loading
programs into the internal RAM and executing them. This is a versatile mode because there are
essentially no limitations on the special-purpose program that is boot-loaded into the internal RAM.
A.7.1 Mode Entry
Mode entry is done at the rising edge of the RESET pin. Once the device enters one of the modes, the
mode cannot be changed by software. Only an external reset can change the mode.
At the rising edge of the RESET pin, the device latches the states of IRQ1 and IRQ2 and places itself in
the specified mode. While the RESET pin is low, all pins are configured as single-chip mode.
shows the states of IRQ1 and IRQ2 for each mode entry.
High voltage V
A.7.2 Single-Chip Mode (SCM)
In this mode, all address and data bus activity occurs within the MCU. Thus, no external pins are required
for these functions. The single-chip mode allows the maximum number of I/O pins for on-chip peripheral
functions, for example, ports A through E, and LCD drivers.
Freescale Semiconductor
Single-chip (user) mode
Bootstrap mode
TST
RESET
IRQ2
IRQ1
V
TST
= 2 x V
= 2 x V
DD
DD
Modes
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
is required to select modes other than single-chip mode.
Table A-3. Mode Select Summary
Figure A-3. Mode Entry Diagram
SINGLE-CHIP MODE
RESET
V
PC6/IRQ1
SS
V
or V
TST
DD
V
PC7/IRQ2
SS
V
or V
DD
DD
Modes of Operation
V
V
V
V
V
V
V
TST
DD
SS
DD
SS
DD
SS
Table A-3
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