MC68HC000FN12 查看數據表（PDF） - Motorola => Freescale

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MC68HC000FN12

Addendum to M68000 User Manual

Motorola => Freescale 

power consumption to its quiescent value1 while maintaining the internal state of the processor. The

low-power mode described below will be routinely tested as part of the MC68SEC000 test vectors provided

by Motorola.

To successfully enter the low-power mode, the MC68SEC000 must first be in the supervisor mode. A

recommended method for entering the low-power mode is to use the TRAP instruction, which causes the

processor to begin exception processing, thus entering the supervisor mode. External circuitry should

accomplish the following steps during the trap routine:

1. Externally detect a write to the low-power address. You select this address which can be any address

in the 16 Mbyte addressing range of the MC68SEC000. A write to the low-power address can be

detected by polling A23–A0, R/W, and FC2–FC0. When the low-power address is detected, R/W is

a logic low, and the function codes have a five (101) on their output, the processor is writing to the

low-power address in supervisor mode and user-designed circuitry should assert the

ADDRESS_MATCH signal shown in Figure 2 and Figure 3.

ADDRESS_MATCH

AS

DQ

CK AS

Q

CL

DQ

CK

Q

CL

DQ

CK

Q

CPU_CLK

RESTART

RESET

SYSTEM_CLK

Figure 2. MC68SEC000 Low-Power Circuitry for 16-Bit Data Bus

ADDRESS_MATCH

AS

DQ

CK

AS

Q

CL

DQ

CK

AS

Q

CL

DQ

CK

Q

CL

DQ

CK

Q

CPU_CLK

RESTART

RESET

SYSTEM_CLK

Figure 3. MC68SEC000 Low-Power Circuitry for 8-Bit Data Bus

2. Execute the STOP instruction. The external circuitry shown in Figure 2 and Figure 3 will count the

number of bus cycles starting with the write to the low-power address and will stop the processor

clock on the first falling edge of the system clock after the bus cycle that reads the immediate data

of the STOP instruction. Figure 3 has one more flip-flop than Figure 2 because the MC68SEC000 in

1. The preliminary specification for the MC68SEC000’s current drain while in the low-power mode is Idd < 2µA for 3.3V operation and

Idd < 5µA for 5.0V operation.

5

M68000 USER’S MANUAL ADDENDUM

MOTOROLA

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