Figure C-10SUBCY Instruction | Xilinx UG129 guide

R

Appendix : PicoBlaze Instruction Set and Event Reference

Pseudocode

sX Å (sX – Operand) mod 256; always an 8-bit result

if ( (sX – Operand) < 0 ) then

CARRY Å 1 else

CARRY Å 0 endif

if ( (sX - Operand) = 0 ) then

ZERO Å 1 else

ZERO Å 0 endif

PC Å PC + 1

Registers/Flags Altered

Registers: sX, PC

Flags: CARRY, ZERO

SUBCY sX, Operand —Subtract Operand from Register sX with Borrow

The SUBCY instruction performs an 8-bit subtraction of two operands and subtracts an additional ‘1’ if the CARRY (borrow) flag was set by a previous instruction, as shown in Figure C-10. The first operand is any register, which also receives the result of the operation. The second operand is also any register or an 8-bit constant value. Flags are affected by this operation.

	Register sY or
	Literal kk
Borrow	Borrow In
CARRY	Register sX
	UG129_aC_04_051604

Figure C-10:SUBCY Instruction

Examples

Operand is a register location, sY, or an immediate byte-wide constant, kk.

SUBCY sX, sY; Subtract register. sX = sX - sY - CARRY

SUBCY sX, kk; Subtract immediate. sX = sX - kk - CARRY

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PicoBlaze 8-bit Embedded Microcontroller

UG129 (v1.1.2) June 24, 2008

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Xilinx UG129 manual Figure C-10SUBCY Instruction

Contents

PicoBlaze 8-bit Embedded Microcontroller User Guide UG129 v1.1.2 June 24 Revision History Version Revision Limitation of Liability Limited Warranty and DisclaimerLimitations 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 Instruction Program Store PicoBlaze Microcontroller Functional BlocksGeneral-Purpose Registers Introduction Byte Scratchpad RAM Arithmetic Logic Unit ALUFlags Input/Output Program Flow Control ResetProgram Counter PC CALL/RETURN Stack Why the PicoBlaze Microcontroller? Why Use a Microcontroller within an FPGA?Why the PicoBlaze Microcontroller? Strengths Weaknesses PicoBlaze Interface Signals PicoBlaze Interface Signal DescriptionsSignal Direction Description Readstrobe PicoBlaze Instruction Set 1PicoBlaze Instruction Set alphabetical listing Enable Interrupt Returni Disable Address Spaces Instruction 1Kx18 Direct Processing Data Logic InstructionsPicoBlaze Instruction Set 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 Direct Addressing Scratchpad RAMAddress Modes Indirect Addressing Implementing a Look-Up Table Scratchpad RAM Stack Operations Fifo OperationsStack Operations Scratchpad RAM Input and Output Ports Portid Port Input Operations 1INPUT Operation and Fpga Interface Logic INPORT70 Input OperationsPORTID70 Register s0 Applications with Few Input Sources Readstrobe Interaction with FIFOsInput and Output Ports 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 Predicting Executing Performance PerformanceInput Clock Frequency Frequency Performance PicoBlaze Development Tools Assembler Assembly Errors Input and Output FilesPicoBlaze Development Tools 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 Differences Between the KCPSM3 Assembler and pBlazIDEDirectives Function KCPSM3 Directive PBlazIDE Directive PicoBlaze Development Tools Using the PicoBlaze Microcontroller in an Fpga Design Vhdl Design FlowKCPSM3 Module Connecting the Program ROM Using the PicoBlaze Microcontroller in an Fpga Design Generating an ESC Schematic Symbol Black Box Instantiation of KCPSM3 using KCPSM3.ngcGenerating the Program ROM using progrom.coe Black Box Instantiation of KCPSM3 using KCPSM3.ngc Using the PicoBlaze Microcontroller in an Fpga Design Assembler Directives Locating Code at a Specific AddressNaming or Aliasing Registers Defining I/O Ports pBlazIDE Defining ConstantsNaming the Program ROM Output File PBlazIDE Input Ports Output PortsDefining I/O Ports pBlazIDE 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 2pBlazIDE Simulator Control Buttons Function Assemble Simulator Control ButtonsInstruction Set Simulation with pBlazIDE Edit Run to Cursor RunStep Over 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 Enable Interrupt Enable External Interrupt InputDisable Interrupt Disable 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 Reset Event Reset EventTable C-3PicoBlaze Reset Values Resource Reset Event Effect Table C-4RETURN Instruction Conditions Description PBlazIDE Equivalent RET, RET C, RET NC, RET Z, RET NZ Table C-5Rotate Left RL Operation RL sX Rotate Left Register sXRR sX Rotate Right Register sX Table C-6Rotate Right RR Operation SL 0 1 X a sX Shift Left Register sX SL 0 1 X a sX Shift Left Register sXTable C-7Shift Left Operations 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 Register and Scratchpad RAM Planning Worksheets RegistersReg Description Scratchpad RAM Appendix Register and Scratchpad RAM Planning WorksheetsLoc Description