dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 103

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

4.2.4.3
When the peripheral registers are mapped to the last 64 locations in X memory, these can be accessed with
short addressing mode. For the I/O short addressing mode, the address of the operand occupies 6 bits in the
instruction operation word and is one-extended. This allows direct access to the last 64 locations in X
memory, which may contain the on-chip peripheral registers. No registers are used to form the address of
the operand. See Figure 4-14 for examples of using the I/O short direct addressing mode. Note that when
peripherals are connected to the DSP56800 core using the Freescale-standard IP-BUS (or PGDB)
interface, peripheral registers may be mapped into any other data (X) memory range. Note that if the
peripheral registers are mapped to an area of memory outside the range X:$FFC0-X:$FFFF, this address
mode will not be available and the registers are then accessed with other suitable standard addressing
mode.
4.2.5
Some instructions make implicit reference to the program counter (PC), software stack, hardware stack
(HWS), loop address register (LA), loop counter (LC), or status register (SR). The implied registers and
their use are defined by the individual instruction descriptions. See Appendix A, “Instruction Set Details,“
for more information.
4.2.6
Table 4-8 on page 4-24 contains a summary of the addressing modes discussed in the preceding
subsections of Section 4.2.
Freescale Semiconductor
Implicit Reference
Addressing Modes Summary
Assembler syntax: X:<pp>
Additional instruction execution cycles: 0
Additional effective address program words: 0
I/O Short Address (Direct Addressing): <pp>
$FFFB
$FFFF
R3
Memory Mapped Registers
I/O Short Address Example
15
15
Before Execution
5
Figure 4-14. Special Addressing: I/O Short Address
6
XXXX
7
8
0
0
Address Generation Unit
: MOVE X:<<$FFFB,R3
$FFFB
$FFFF
R3
Memory Mapped Registers
15
15
5
After Execution
$5678
6
7
8
0
0
Addressing Modes
AA0027
4-23