Lucent Technologies DSP1611, Information Manual

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Information Manual DSP1611/17/18/27/28/29 DIGITAL SIGNAL PROCESSOR
April 1998 External Memory Interface
Lucent Technologies Inc.
DRAFT COPY
6-25
6.5 Boot-Up from External ROM
After RSTB goes from low to high, the DSP comes out of reset and fetches an instruction from location zero of the
instruction/coefficient space memory map in effect. If the EXM pin is high at the rising edge of RSTB, MAP2 is
selected. If MAP2 is selected, EROM enable goes low because MAP2 has EROM at location zero. If the external
memory device is slow, the mwait register can be initialized with all the external memory segments having 15 wait-
states by setting the INT1 external pin low. As the program executes, it can reset the wait-states to a more appro-
priate value. If both EXM and INT1 are high and RSTB goes high, DSP uses MAP2 with zero wait-states.
When emerging from the reset sequence, the EROM enable goes low to fetch the first instruction at location zero.
The first instruction is actually fetched twice, and only the second value is used.
Figure 6-11 shows a flow chart of
the initialization.
5-4170
Figure 6-11. External ROM Boot-Up
SELECT
MAP 2
EXM
HIGH
?
SELECT
MAP 1
INTERNAL
ROM
INT1
LOW ?
WAIT-
STATES = 15
YES
WAIT-
STATES = 0
FETCH INSTR.
TWICE FROM
EROM, ADDR0
YES NO
NO
RSTB
GOES HIGH