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3-14 Optimizing DSP56300/DSP56600 Applications MOTOROLA

Program Control

PC Relative Instructions

In absolute addressing, the argument is the numerical value of the

address. In PC relative addressing, the argument is the

displacement of the address relative to the PC. For both absolute

and PC addressing, the address argument could be specified in one

of four ways:

1. explicit, as part of the 1-word opcode (restricted to short

arguments),

2. explicit, as a second program word ,

3. stored in a register , or,

4. indirect, stored in the memory and accessed by one of the

addressing modes <ea>.

A full list of instructions requiring a program location argument

and the possible addressing modes for each is summarized in

Table 3-5. The shaded sections in the table indicate instructions that

use PC relative arguments.

Note: The instructions LRA (load PC relative address) and LUA

(load effective address) can be used to calculate and load PC

relative address or an effective address, respectively. LRA is

a very efficient and common way for a program to monitor

directly the PC value during runtime.

Note: The DSP56600 does not include the complete set of

PC-Relative instructions like the DSP56300. There is also a

way to disable all the PC-Relative instructions on the

DSP56600 by setting a special mode bit, the PCD (PC relative

logic Disable) which is Bit 5 in the Operating Mode Register

(OMR). For details please see the

DSP56600 Family Manual

Table 3-5 Instructions with Program Memory Arguments

Function

Address

Argument

Mnemonic

The Address Argument

Encoded in the

opcode

(total 1 w)

2nd

word

Memory

<ea>

unconditional

jump

destination

JMP addr < 4096 + – +

BRA –257 <

disp < 256

+ + –

jump on CCR

condition

destination

Jcc address <

4096

+– +

Bcc –257 <

disp < 256

+ + –

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 111 112

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