Processor Initialization, Resets, and Clocking

3.3Reset modes

The reset signals in the processor enable you to reset different parts of the design independently. Table 3-1shows the reset signals, and the combinations and possible applications that you can use them in.

 

 

 

 

 

Table 3-1 Reset modes

 

 

 

 

 

 

Reset mode

nRESET

PRESETDBGn

nSYSPORESET

nCPUHALT

Application

 

 

 

 

 

 

Power-on reset

0

x

0

x

Reset at power up, full system

 

 

 

 

 

reset. Hard reset or cold reset.

 

 

 

 

 

 

Processor reset

0

x

1

x

Reset of processor only,

 

 

 

 

 

watchdog reset. Soft reset or

 

 

 

 

 

warm reset.

 

 

 

 

 

 

Normal

1

x

1

1

Normal run mode.

 

 

 

 

 

 

Halt

1

x

1

0

Halt mode, provided normal

 

 

 

 

 

mode has not been entered

 

 

 

 

 

since reset.

 

 

 

 

 

 

Debug reset

x

0

x

x

Resets all debug logic and

 

 

 

 

 

debug APB interface.

 

 

 

 

 

 

Note

If nRESET is set to 1 and nSYSPORESET is set to 0 the behavior is architecturally

Unpredictable.

This section of the manual describes:

Power-on reset

Processor reset on page 3-8

Normal operation on page 3-8

Halt operation on page 3-8.

3.3.1Power-on reset

You must apply power-on or cold reset to the processor when power is first applied to the system. In the case of power-on reset, the leading, or falling, edge of the reset signals, nRESET and nSYSPORESET, does not have to be synchronous to CLKIN. Because the nRESET and nSYSPORESET signals are synchronized within the processor, you do not have to synchronize these signals. Figure 3-1shows the application of power-on reset.

CLKIN

nRESET

nSYSPORESET

Figure 3-1 Power-on reset

ARM recommends that you assert the reset signals for at least four CLKIN cycles to ensure correct reset behavior.

It is not necessary to assert PRESETDBGn on power-up.

ARM DDI 0363E

Copyright © 2009 ARM Limited. All rights reserved.

3-7

ID013010

Non-Confidential, Unrestricted Access

 

Page 82
Image 82
ARM R4F, r1p3 manual Reset modes, Power-on reset