Setting and Clearing Carry Flag, Test and Compare | Xilinx UG129

R

Chapter 3: PicoBlaze Instruction Set

A similar NOP technique is to simply jump to the next instruction, which is equivalent to the default program flow. The JUMP instruction consumes an instruction cycle (two clock cycles) without affecting register contents.

JUMP next

next: <next instruction>

Figure 3-19:Alternative NOP Method Using JUMP Instructions

Setting and Clearing CARRY Flag

Sometimes, application programs need to specifically set or clear the CARRY flag, as shown in the following examples.

Clear CARRY Flag

ANDing a register with itself clears the CARRY flag without affecting the register contents, as shown in Figure 3-20.

clear_carry_bit:

AND sX, sX ; register sX unaffected, CARRY flag cleared

Figure 3-20:ANDing a Register with Itself Clears the CARRY Flag

Set CARRY Flag

There are various methods for setting the CARRY flag, one of which appears in

Figure 3-21. Generally, these methods affect a register location.

set_carry: LOAD sX, 00

COMPARE sX, 01 ; set CARRY flag and reset ZERO flag

Figure 3-21:Example Operation that Sets the CARRY Flag

Test and Compare

The PicoBlaze microcontroller introduces two new instructions not available on previous PicoBlaze variants. The PicoBlaze microcontroller provides the ability to test individual bits within a register and the ability to compare a register value against another register or an immediate constant. The TEST or COMPARE instructions only affect the ZERO and CARRY flags; neither instruction affects register contents.

Test

The TEST instruction performs bit testing via a bitwise logical AND operation between two operands. Unlike the AND instruction, only the ZERO and CARRY flags are affected; no registers are modified. The ZERO flag is set if all the bitwise AND results are Low, as shown in Figure 3-22.

32	www.xilinx.com	PicoBlaze 8-bit Embedded Microcontroller
		UG129 (v1.1.2) June 24, 2008

Image 32

Xilinx UG129 manual Setting and Clearing Carry Flag, Test and Compare

Contents

PicoBlaze 8-bit Embedded Microcontroller User Guide UG129 v1.1.2 June 24 Revision History Version Revision Limited Warranty and Disclaimer LimitationsLimitation of Liability Technical Support Limitations Acknowledgments Preface Acknowledgments Guide Contents About This Guide Preface About This Guide Table of Contents Interrupts Performance Appendix C PicoBlaze Instruction Set and Event Reference PicoBlaze Microcontroller Features Introduction PicoBlaze Microcontroller Functional Blocks General-Purpose RegistersInstruction Program Store Introduction Arithmetic Logic Unit ALU FlagsByte Scratchpad RAM Input/Output Reset Program Counter PCProgram Flow Control CALL/RETURN Stack Why the PicoBlaze Microcontroller? Why the PicoBlaze Microcontroller?Why Use a Microcontroller within an FPGA? Strengths Weaknesses Signal Direction Description PicoBlaze Interface SignalsPicoBlaze Interface Signal Descriptions Readstrobe PicoBlaze Instruction Set 1PicoBlaze Instruction Set alphabetical listing Enable Interrupt Returni Disable Address Spaces Instruction 1Kx18 Direct PicoBlaze Instruction Set Processing DataLogic Instructions 2Complementing a Register Value 3Inverting an Individual Bit Location 616-Setting a Bit Location Arithmetic Instructions SUB and Subcy Subtract Instructions Multiplication 10Incrementing and Decrementing a Register 148-bit by 8-bit Multiply Routine Produces a 16-bit Product 168-bit by 8-bit Multiply Routine Using Hardware Multiplier Division No Operation NOP 18Loading a Register with Itself Acts as a NOP Instruction Setting and Clearing Carry Flag Test and Compare 22The Test Instruction Affects the Zero Flag 25Generate Parity for a Register Using the Test Instruction Shift and Rotate Instructions SRX 5PicoBlaze Rotate Instructions Rotate Left Rotate Right Moving Data Program Flow Control Program Flow Control 6Instruction Conditional Execution Description CALL/RETURN Program Flow Control UG129 v1.1.2 June 24 Interrupts 1Simple Interrupt Logic Example Interrupt Flow 2Example Interrupt Flow 3Interrupt Timing Diagram Example Interrupt Flow Interrupts Scratchpad RAM Address ModesDirect Addressing Indirect Addressing Implementing a Look-Up Table Scratchpad RAM Stack Operations Stack OperationsFifo Operations Scratchpad RAM Input and Output Ports Portid Port Input Operations 1INPUT Operation and Fpga Interface Logic Input Operations PORTID70INPORT70 Register s0 Input and Output Ports Applications with Few Input SourcesReadstrobe Interaction with FIFOs Output Operations Output Operations Simple Output Structure for Few Output Destinations Fpga Register 8Use Constant Directives to Declare Output Port Addresses Pipelining for Maximum Performance 9Pipelining the Portid Decoding Improves Performance Pipelining for Maximum Performance Repartitioning the Design for Maximum Performance Effective Pipelining Improves Read Performance Instruction Storage Configurations Standard Configuration Single 1Kx18 Block RAM Instruction Storage Configurations Two PicoBlaze Microcontrollers Share a 1Kx18 Code Image 6Using Distributed ROM for Instruction Memory Distributed ROM Instead of Block RAM Instruction Storage Configurations Performance Input Clock FrequencyPredicting Executing Performance Frequency Performance PicoBlaze Development Tools Assembler PicoBlaze Development Tools Assembly ErrorsInput and Output Files Configuring pBlazIDE for the PicoBlaze Microcontroller Mediatronix pBlazIDE Importing KCPSM3 Code into pBlazIDE 4Example of How Kcpsm Source Code Converts to pBlazIDE Code Differences Between the KCPSM3 Assembler and pBlazIDE DirectivesDifferences Between the KCPSM3 Assembler and pBlazIDE Function KCPSM3 Directive PBlazIDE Directive PicoBlaze Development Tools KCPSM3 Module Using the PicoBlaze Microcontroller in an Fpga DesignVhdl Design Flow Connecting the Program ROM Using the PicoBlaze Microcontroller in an Fpga Design Black Box Instantiation of KCPSM3 using KCPSM3.ngc Generating the Program ROM using progrom.coeGenerating an ESC Schematic Symbol Black Box Instantiation of KCPSM3 using KCPSM3.ngc Using the PicoBlaze Microcontroller in an Fpga Design Naming or Aliasing Registers Assembler DirectivesLocating Code at a Specific Address Defining Constants Naming the Program ROM Output FileDefining I/O Ports pBlazIDE PBlazIDE Defining I/O Ports pBlazIDE Input PortsOutput Ports Input/Output Ports 5Example of pBlazIDE Dsout Directive Custom Instruction Op-Codes Custom Instruction Op-Codes Assembler Directives Simulating PicoBlaze Code Instruction Set Simulation with pBlazIDE Simulator Control Buttons Instruction Set Simulation with pBlazIDE2pBlazIDE Simulator Control Buttons Function Assemble Edit Run Step OverRun to Cursor Pause Turbocharging Simulation using FPGAs Turbocharging Simulation using FPGAs Simulating PicoBlaze Code Related Materials and References Chapter Related Materials and References Example Program Templates KCPSM3 Syntax PBlazIDE Syntax Appendix Example Program Templates PicoBlaze Instruction Set and Event Reference ADD sX, Operand -Add Operand to Register sX Addcy sX, Operand -Add Operand to Register sX with Carry Appendix PicoBlaze Instruction Set and Event Reference SX, Operand Logical Bitwise and Register sX with Operand SX, Operand Logical Bitwise and Register sX with Operand Examples Condition Table C-1CALL Instruction Conditions Description Compare sX, Operand Compare Operand with Register sX Figure C-4COMPARE Operation Disable Interrupt Disable External Interrupt Input Disable Interrupt Disable External Interrupt InputEnable Interrupt Enable External Interrupt Input Figure C-5FETCH Operation KCPSM3 Instruction PBlazIDE Instruction Portid Å Operand SX Å Inport PC Å PC + Interrupt Event, When Enabled Table C-2JUMP Instruction Conditions Description Load sX, Operand Load Register sX with Operand Or sX, Operand Logical Bitwise or Register sX with Operand Or sX, Operand Logical Bitwise or Register sX with Operand Figure C-7OUTPUT Operation and Fpga Interface Logic Table C-3PicoBlaze Reset Values Resource Reset Event Effect Reset EventReset Event Table C-4RETURN Instruction Conditions Description PBlazIDE Equivalent RET, RET C, RET NC, RET Z, RET NZ RL sX Rotate Left Register sX RR sX Rotate Right Register sXTable C-5Rotate Left RL Operation Table C-6Rotate Right RR Operation Table C-7Shift Left Operations SL 0 1 X a sX Shift Left Register sXSL 0 1 X a sX Shift Left Register sX SR 0 1 X a sX Shift Right Register sX Shift Right with ‘ 0’ fill Figure C-8STORE Operation SUB sX, Operand -Subtract Operand from Register sX Store sX, sY Figure C-10SUBCY Instruction Registers sX Flags CARRY, Zero PBlazIDE Equivalent Subc Figure C-11ZERO Flag Logic for Test Instruction PicoBlaze 8-bit Embedded Microcontroller 117 XOR sX, Operand Logical Bitwise XOR Register sX with Operand Instruction Codes Table D-1PicoBlaze Instruction Codes Jump Z PicoBlaze 8-bit Embedded Microcontroller 121 Appendix Instruction Codes Reg Description Register and Scratchpad RAM Planning WorksheetsRegisters Loc Description Scratchpad RAMAppendix Register and Scratchpad RAM Planning Worksheets