MC68HC05L16 Datasheet, PDF (135/146 Pages) Freescale Semiconductor, Inc – Microcontrollers

Modes of Operation
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. Table A-3
shows the states of IRQ1 and IRQ2 for each mode entry.
High voltage V_TST = 2 x V_DD is required to select modes other than single-chip mode.
Table A-3. Mode Select Summary
Modes
RESET
PC6/IRQ1
PC7/IRQ2
Single-chip (user) mode
Bootstrap mode
V_SS or V_DD
V_TST
V_SS or V_DD
V_DD
SINGLE-CHIP MODE
RESET
V_DD
V_SS
V_TST
V_DD
IRQ1
V_SS
V_DD
IRQ2
V_SS
V_TST = 2 x V_DD
Figure A-3. Mode Entry Diagram
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.
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
Freescale Semiconductor
135