Operating Modes; Dsp56303 Operating Modes - Motorola DSP56303 User Manual

Operating Modes

4.1 Operating Modes
The DSP56303 begins operation by leaving the Reset state and going into one of eight
operating modes. As the DSP56303 exits the Reset state, it loads the values of
, and into bits MA, MB, MC, and MD of the OMR. These bit settings determine
MODC MODD
the chip's operating mode, which in turn determines the bootstrap program option the chip
uses to start up. Software can also set the OMR[MA–MD] bits directly. A jump directly to the
bootstrap program entry point ($FF0000) after the OMR bits are set causes the DSP56303 to
execute the specified bootstrap program option (except modes 0 and 8). Table 4-1 shows the
DSP56303 bootstrap operation modes, the corresponding settings of the external operational
mode signal lines (the OMR[MA–MD] bits), and the reset vector address to which the
DSP56303 jumps once it leaves the Reset state.
Mode MODD MODC
0 0 0
1 0 0
4-2
Table 4-1. DSP56303 Operating Modes
Reset
MODB MODA
Vector
0 0 $C00000
0 1 $FF0000
DSP56303 User's Manual
Description
Expanded mode
Bypasses the bootstrap ROM, and the DSP56303
starts fetching instructions beginning at address
$C00000. Memory accesses are performed using
SRAM memory access type with 31 wait states and
no address attributes selected (default). Address
$C00000 is reflected as address $00000 on Port A
signals A[0–17].
Bootstrap from byte-wide memory
The bootstrap program it loads a program RAM
segment from consecutive byte-wide P memory
locations, starting at P:$D00000 (bits 7-0). The
memory is selected by the Address Attribute AA1
and is accessed with 31 wait states. The EPROM
bootstrap code expects to read 3 bytes specifying
the number of program words, 3 bytes specifying the
address to start loading the program words and then
3 bytes for each program word to be loaded. The
number of words, the starting address and the
program words are read least significant byte first
followed by the mid and then by the most significant
byte. The program words are condensed into 24-bit
words and stored in contiguous PRAM memory
locations starting at the specified starting address.
After reading the program words, program execution
starts from the same address where loading started.
, ,
MODA MODB