System Interface9
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9.7.5.5 BDMA Port During Powerdown (ADSP-2181)
Do not powerdown the ADSP-2181 during a BDMA transfer. If you do, the
DSP will not be able to recover correctly from powerdown and the contents of
memory accessed by the ADSP-2181’s BDMA port will be corrupted.
If you need to go into powerdown mode, either:
• Verify that the BWCOUNT register contains a zero. If a BDMA transfer is in
process, poll the BWCOUNT register to determine when the transfer is done.
or
• Abort any BDMA transfer in progress by writing 1 to the BWCOUNT
register and go into powerdown when the BWCOUNT register contains a
zero. (Note that the BDMA transfer is not properly completed in this case.)
9.7.5.6 Analog Interface (ADSP-21msp5x)
You must powerdown the ADSP-21msp58/59’s analog interface separately
from the processor, as described in the Analog Interface chapter of this manual.
The analog interface does not work during powerdown and causes additional
power to be dissipated if it is not disabled. The following code example shows
a powerdown interrupt routine for the ADSP-21msp58/59:
{ Sample Powerdown Code }
{ located at address 0x002C }
pwd_int: ax0 = 0x0000; {powerdown analog interface}
dm(0x3FEE) = ax0;
ax0 = 0x0000; {enable crystal, no delay}
dm(0x3FEF) = ax0;
NOP;
idle;
rti;
It takes three cycles for the analog interface to powerdown. The IDLE
instruction should not be executed before these three cycles have elapsed.
9.7.6 Conditions For Lowest Power Consumption
The state of all processor pins during powerdown is shown in Table 9.9.
To assure the lowest power consumption, all active input pins should be held
at a CMOS level. All active output pins should be free of resistive load since
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