MC68HC711D3CFNE2 Datasheet, PDF (40/124 Pages) Freescale Semiconductor, Inc – Power Saving STOP and WAIT Modes

Freescale Semiconductor, Inc.
In the second method, the MODB/V_STBY pin can supply RAM power from a battery
backup or from a second power supply, as shown in Figure 4-3. Using the MODB/
V_STBY pin may require external hardware, but can be justified when a significant
amount of external circuitry is operating from V_DD. If V_STBY is used to maintain RAM
contents, reset must be held low whenever V_DD is below normal operating level. Refer
to SECTION 5 RESETS AND INTERRUPTS.
V_DD
4.8 V
NiCd +
MAX
690
V_DD
V_OUT
V_BATT
4.7k
TO MODB/V_STBY
OF M68HC11
MODB/VSTBY CONN
Figure 4-3 RAM Standby MODB/V_STBY Connections
4.2.1 Priority and Mode Select Register
The four operating modes are selected with the logic states of the mode A (MODA)
and mode B (MODB) pins during reset. The MODA and MODB logic levels determine
the logic state of the special mode (SMOD) and mode A (MDA) control bits in the
HPRIO register.
After reset is released, the mode select pins no longer influence the MCU operating
mode. For single-chip mode, the MODA pin is connected to a logic zero. For expanded
mode, MODA is normally connected to V_DD through a pull-up resistor of 4.7 kΩ. The
MODA pin also functions as the load instruction register (LIR) pin when the MCU is not
in reset. The open drain active low LIR output pin drives low during the first E cycle of
each instruction. The MODB pin also functions as standby power input, V_STBY, which
maintains RAM contents in the absence of V_DD. Refer to Table 4-2 for information
about hardware mode selection.
MODB
1
1
0
0
Table 4-2 Hardware Mode Select Summary
Inputs
MODA
0
1
0
1
Mode
Single-Chip
Expanded Multiplexed
Special Bootstrap
Special Test
RBOOT
0
0
1
0
Latched at Reset
SMOD MDA
0
0
0
1
1
0
1
1
OPERATING MODES AND ON-CHIP MEMORY
4-6
TECHNICAL DATA
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