Vault 7: Projects

This publication series is about specific projects related to the Vault 7 main publication.

16-bit MCU and DSC Programmer’s Reference Manual
DS70157F-page 146 © 2005-2011 Microchip Technology Inc.
BRA OA
Branch if Overflow Accumulator A
Implemented in: PIC24F PIC24H PIC24E dsPIC30F dsPIC33F dsPIC33E
X X X
Syntax: {label:} BRA OA, Expr
Operands: Expr may be a label, absolute address or expression.
Expr is resolved by the linker to a Slit16, where
Slit16 [-32768 ... +32767].
Operation: Condition = OA
If (Condition)
(PC + 2) + 2 * Slit16 PC
NOP Instruction Register
Status Affected: None
Encoding: 0000 1100 nnnn nnnn nnnn nnnn
Description: If the Overflow Accumulator A flag is ‘1’, then the program will branch
relative to the next PC. The offset of the branch is the two’s complement
number ‘2 * Slit16’, which supports branches up to 32K instructions
forward or backward. The Slit16 value is resolved by the linker from the
supplied label, absolute address or expression.
If the branch is taken, the new address will be (PC + 2) + 2 * Slit16, since
the PC will have incremented to fetch the next instruction. The instruction
then becomes a two-cycle instruction, with a NOP executed in the second
cycle.
The ‘n’ bits are a signed literal that specifies the number of instructions
offset from (PC + 2).
Note: The assembler will convert the specified label into the offset to
be used.
Words: 1
Cycles: 1 (2 if branch taken) – dsPIC30F, dsPIC33F
1 (4 if branch taken)dsPIC33E
Example 1:
002000 HERE: BRA OA, BYPASS
002002 NO_OA: . . .
002004 . . .
002006 . . .
002008 . . .
00200A GOTO THERE
00200C BYPASS: . . .
00200E . . .
; If OA, branch to BYPASS
; Otherwise... continue
Before
Instruction
After
Instruction
PC 00 2000 PC 00 200C
SR 8800 (OA, OAB = 1) SR 8800 (OA, OAB = 1)

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