Program Loops Djnz | Texas Instruments MSC1210 instruction

Program Loops (DJNZ)

16.11 Program Loops (DJNZ)

Many operations are conducted within finite loops. That is, a given code seg- ment is executed repeatedly until a given condition is met.

A common type of loop is a simple counter loop. This is a code segment that is executed a certain number of times and then finishes. This is accomplished easily in 8052 assembly language with the DJNZ instruction. DJNZ means decrement, jump if not zero. Consider the following code:

MOV R0,#08h ;Set number of loop cycles to 8

LOOP: INC A ;Increment accumulator (or do whatever ;the loop does)

DJNZ R0,LOOP ;Decrement R0, loop back to LOOP if R0 ;is not 0

DEC A ;Decrement accumulator (or whatever you ;want to do)

This is a very simple counter loop. The first line initializes R0 to 8, which is the number of times the loop will be executed.

The second line labeled LOOP, is the actual body of the loop. This could con- tain any instruction or instructions you wishe to execute repeatedly. In this case, the accumulator is incremented with the INC A instruction.

The interesting part is the third line with the DJNZ instruction. This instruction says to decrement the R0 Register, and if it is not now zero, jump back to LOOP. This instruction decrements the R0 register, then checks to see if the new value is zero and, if not, will go back to LOOP. The first time this loop exe- cutes, R0 is decremented from 08 to 07, then from 07 to 06, and so on until it decrements from 01 to 00. At that point, the DJNZ instruction fails because the accumulator is zero. That causes the program to not go back to LOOP, and thus, it continues executing with the DEC instruction—or whatever you want the program to do after the loop is complete.

DJNZ is one of the most common ways to perform programming loops that ex- ecute a specific number of times. The number of times the loop is executed depends on the initial value of the R register that is used by the DJNZ instruc- tion.

16-12

Image 206

Texas Instruments MSC1210 manual Program Loops Djnz

Contents

User’s Guide Important Notice Basic Registers Introduction to the MSC1210MSC1210 Memory Organization Serial Communication Addressing ModesSystem Timing Pulse Width Modulator/Tone Generator Analog-to-Digital Converter Serial Peripheral Interface SPI Additional MSC1210 Hardware Additional Resource Boot ROM Routines Additional Features in the MSC1210 Compared toClock Timing Diagram Instruction-Set Quick-Reference Guide SPI/PWM/Flash Write Timing System Timing Interrupt Control 16−1 Pin Descriptions of the MSC1210 14−2 Chapter −1. MSC1210 Block Diagram MSC1210 Description −2. Pin Configuration of the MSC1210 MSC1210 Pin-Out −1. Pin Descriptions of the MSC1210 Pin # Name Description −1 Pin Descriptions of the MSC1210 Pin # Name Description 1 I/O Ports P0, P1, P2, and P3 AD7 Port Port Oscillator Inputs XTAL1 and XTAL2 Program Store Enable Psen Reset Line RSTAddress Latch Enable ALE External Access EA Enhanced 8051 Core −3. MSC1210 Timing Compared to Standard 8051 Timing High Performance Analog Functions Family Device CompatibilityFlash Memory High-Performance Peripherals Description Program Memory Data Memory Internal RAM Description Program Memory −1. Program and Data Memory Size MSC1210Y2 MSC1210Y3 MSC1210Y4 MSC1210Y5 On-Chip Extended Static RAM Sram Data Memory−2. Program and Data Memory Addresses On-Chip Flash Data Memory External Data Memory Internal RAM −2. MSC1210 Memory Map Register Bank Stack Register Banks Bit Memory Or execute Special Function Register SFR Memory Defines the MSC1210 SFRs −1. SFR Names and Addresses SCON0 Referencing SFRs Referencing Bits of SFRs Bit−Addressable SFRs SFR Types SFR Definitions SFR Definitions SFR Definitions SFR Definitions Can be generated automatically by the MSC1210 P0DDRL/P0DDRH Port 0 Data Direction Low/High Byte, Addresses GCL/GCM/GCH Gain Low/Middle/High Byte, Addresses D4H/D5H/D6H SFR Definitions SFR Definitions SFR Definitions Describes the basic register functions of the MSC1210 ADC Accumulator Registers Register Program Counter PC Data Pointer DPTR0/DPTR1 Stack Pointer SP Describes the various addressing modes of the MSC1210 −1. MSC1210 Addressing Modes Mode ExampleImmediate Addressing Direct Addressing Indirect Addressing External Direct Addressing Movx A,@DPTR Movx @DPTR,A External Indirect Addressing Code Indirect Adressing Describes the program flow of the MSC1210 ADC Conditional Branching Direct Jumps Consider the example Interrupts Direct CallsReturns From Routines Description System Timers Startup Timing −1. Standard 8051 Timing System Timing System Timers −2. MSC1210 Timing Chain and Clock Control Microseconds Timer Milliseconds Timer −4. System Timing Interrupt Control One Hundred Millisecond Clock Startup Timing Normal-Mode Power-On Reset TimingFlash Programming Mode Power-On Reset Timing Symbol Parameter Min Max Unit Psen Describes the timers of the MSC1210 ADC How Long Does a Timer Take to Count? How Does a Timer Count?Using Timers to Measure Time Movx Duration SYS CLKs At 12MHz RD or WR StrobeWidth Width ∝s SFR Name Description SFR Address Bit Addressable? Timer SFRs−1. Timer Conrol SFRs Tmod SFR Mode −2. Timer Modes and Usage TxM1 TxM0 Timer Description of Timer Mode Cycle −3. Example of 8-Bit Auto-ReloadInstruction −4. Tcon 88 H SFR Bit Name Bit Address Explanation of Function TimerTcon SFR Initializing a Timer Reading the Timer Detecting Timer Overflow Timing the Length of Events Using Timers as Event Counters Using Timer 1 T2CON SFR Timer 2 in Auto-Reload Mode Timer 2 in Capture Mode Timer 2 as a Baud Rate Generator Describes serial communication using the MSC1210 ADC Description Setting the Serial Port Mode Function Length Period −1. SM0 and SM1 Function Definitions Mode Serial Mode 0 Synchronous Half-Duplex High four bits bits 4 through 7 are configuration bits −2. Serial Port Mode 0 Receive Timing-High Speed Operation Serial Mode 1 Asynchronous Full-Duplex −3. Serial Port Mode 1 Transmit Timing BaudRate + Timer2Overflow −2. Common Baud Rates Using TimerBaudRate + 32 @ Timer1Overflow BaudRate + 12 @ 256 * TH1 Rcap 2H Rcap 2L + −3. Common Baud Rates Using TimerSerial Mode 2 Asynchronous Full-Duplex Baud Rate RCAP2HRCAP2L @ 11.0592MHz f OSC −6. Serial Port 0 Mode 2 Receive Timing BaudRate + 2SMOD @ fOSC Serial Mode 3 Asynchronous Full-Duplex −7. Serial Port 0 Mode 3 Transmit Timing Setting the Serial Port Mode TH1 = 256 − Crystal / 192 / Baud Setting the Serial Port Baud Rate−4. Mode 0 Commonly Used Baud Rates Baud Rate −5. Baud Rate Settings for Timer Desired Baud Baud Rate 33MHz clk 25MHz clk 11.0592MHz clk Kb/s −6. Baud Rate Settings for TimerWriting to the Serial Port Reading the Serial Port Describes the interrupts of the MSC1210 ADC JNB TF0,SKIPTOGGLE −1.Interrupt Sources Interrupt/Event Addr Priority Flag Enable Priority ControlEvents That Can Trigger Interrupts 10-4 −3.EICON D8 H SFR Enabling Interrupts−2.IE A8 H SFR −4.EIE E8 H SFR Polling Sequence −6.EIP F8 H SFR Interrupt Priorities−5.IP B8 H SFR Interrupt Triggering Exiting Interrupts External Interrupts Types of InterruptsSerial Interrupts −7.EXIF 91 H SFR Bit Name Explanation of Function Auxiliary Interrupts Timer InterruptsWatchdog Interrupt Aux Interrupt Type Method to Clear Interrupt −8.Clearing Auxiliary Interrupts−9.AIE A6 H SFR Bit Name Explanation of Function Clear Interrupt −10. Aistat A7 H SFR−11. PAI A5 H SFR −12. PPI Bits of PAI SFR PAIx Bits Explanation of Interrupt/Event Waking Up from Idle Mode −13. EWU C6 H SFR Register Protection Push PSW Push R0 Error − Invalid instruction Common Problems with Interrupts PWM Generator 11-5 Description 11-2Tone Generator 11-3 −1. Block Diagram Tone Generator ToneFrequency +1 −3. Timing Diagram of Tone Generator in Staircase Mode Tone Generator Waveforms Duty Cycle = PWM Period +1 − PWM Duty/PWM Period +1 PWM Generator−1. PWM Polarity Conditions Condition Duty Cycle −5. Timing Diagram of a PWM Waveform This can be expressed in code as Example of PWM Tone Generation −2. Configuring the PWM for Tone GenerationStmt ‘C’ Source Code Assembly Source Code −3. Statement Explanations Example of PWM Tone Generation Idling Explanation −4. Configuring the PWM for Tone Generation with PWM Idling−5. Statement Explanations Example of Updating PWM −6. PWM Timing 11-12 PGA DAC 12-10 −1. MSC1210 Architecture −2. Input Multiplexer Configuration Input Multiplexer Positive Input Negative Input Temperature Sensor 12-6 Burnout Current Sources MSB @ 10 Input BufferAnalog Input ACLKFrequency −1.PGA Settings Programmable Gain Amplifier PGA Offset DAC Modulator Calibration −2.Calibration Mode Control BitsCalibration Mode Digital Filter −4. Filter Step Responses −5. Filter Frequency Responses −4.Output Data Rate and Channel Rate Multiplexing Channels−3.Filter Settling Samples to Discard Filter Voltage Reference −5.Output Data Rate and Channel Rate 10x faster Summation/Shifter Register Source Summation Count Shift Summation Count Manual Summation Mode ADC Summation Mode Manual Shift Divide Mode ADC Summation with Shift Divide Mode Interrupt-Driven ADC Sampling Analog-to-Digital Converter 12-21 Syncronizing Multiple MSC1210 Devices Analog-to-Digital Converter 12-23 PT100 Ratiometric MeasurementsADC Result + V REF ADC Result + R REF @ I OUT Differential Vref 12-26 SPI System Errors 13-6 Clock Phase and Polarity Controls 13-4SPI Signals 13-5 Description 13-2 −1. SPI block diagram Functional Description −2. SPI Clock/Data Timing Clock Phase and Polarity Controls Master Out Slave SPI SignalsMaster In Slave Out Serial Clock SPI System Errors −3. SPI Reset State Data Transfers 13-8 Fifo Operation −4. SPI Fifo Operation Code Examples SPI Master Transfer in Fifo Mode using Interrupts 13-12 Low-Voltage Detect 14-2 Watchdog Timer 14-4Description 14-2 −1. Brownout Reset and Low-Voltage Detection Low-Voltage Detect −1.Typical Sub-Circuit Current Consumption Power Supply−2.Comparator Specification −3.Band Gap Parameters Watchdog Timer Watchdog Timer Hardware Configuration Enabling Watchdog Timer Watchdog Timer Resetting the Watchdog Timer Disabling Watchdog Timer Watchdog Timeout/Activation Advanced Flash Memory 15-6 Hardware Configuration 15-2Power Optimization 15-9 Breakpoint Generator 15-7 Hardware Configuration Hardware Configuration Registers Hardware Configuration Register 0 HCR0 DFSEL2/1/0 Amount of Flash Data Memory Hardware Configuration Register 1 HCR1 Hardware Configuration Memory Accessing Configuration Memory in a User Program Write Protecting Flash Program Memory Updating Interrupts with Reset Sector LockAdvanced Flash Memory Configuring Breakpoints Breakpoint Generator Breakpoint Auxiliary Interrupt Disabling a Breakpoint Power Optimization Flash Memory as Data Memory Advanced Topics 15-11 Advanced Topics and Other Information Describes the 8052 Assembly Language Syntax Label and instruction Number Bases Expressions −1.Order of Precedence for Mathematical Operators Operator PrecedenceCharacters and Character Strings Order Operator Changing Program Flow LJMP, SJMP, Ajmp Ljmp LABEL3 Subroutines LCALL, ACALL, RET Register Assignment MOV MOV DestinationRegister,SourceValue MOV R2,R1 Invalid MOV @R0,A Incrementing and Decrementing Registers INC, DEC Program Loops Djnz Setting, Clearing, and Moving Bits SETB, CLR, CPL, MOV 16-14 Bit-Based Decisions and Branching JB, JBC, JNB, JC, JNC Value Comparison Cjne Lcall Debouncekey Less Than and Greater Than Comparison Cjne Checkless JC Aisless Zero and Non-Zero Decisions JZ/JNZ Performing Additions ADD, Addc Performing Additions ADD, Addc Performing Subtractions Subb Performing Multiplication MUL Performing Division DIV Shifting Bits RR, RRC, RL, RLC −1. Rotate Operations −3.Results of ORL Bit-Wise Logical Instructions ANL, ORL, XRL−2.Results of ANL −4.Results of XRL Assembly Language 16-25 Exchanging Register Values XCH Swapping Accumulator Nibbles Swap Adjusting Accumulator for BCD Addition DA Using the Stack PUSH/POP Assembly Language 16-29 Setting the Data Pointer Dptr MOV Dptr Reading and Writing External RAM/Data Memory Movx Reading Code Memory/Tables Movc Lcall SUB SUB INC a Using Jump Tables JMP @A+DPTR Describes the Keil simulator and its functions 17-2 Keil Simulator 17-3 Timers −1. Timer/Counter 0 − Mode Timer 0 & 1 Example −2. Timer/Counter −4. Timer/Counter 1 Mode Keil Simulator 17-7 17-8 Keil Simulator 17-9 17-10 Register Bit Toggle Box Name Timer−1.Timer/Counter 2 Control Bits −7. Status of Watchdog Peripheral Watchdog Reset Facility Example 17-14 Keil Simulator 17-15 System Timer Clock Control Analog-to-Digital Converter −8. Analog−to−Digital Converter Peripheral −9. Error Message Summation/Shifter −10. Accumulator/Shifter Peripheral 17.8.1 ADC/Summation/Shifter Example 17-22 Keil Simulator 17-23 17-24 Keil Simulator 17-25 17-26 Keil Simulator 17-27 −11. summation/Shifter Peripheral Keil Simulator 17-29 −13. List Box for the Interrupt Peripheral −14. Parallel Port 0 Contents Display Window Ports Serial Peripheral Interface SPI −16. SPI Peripheral Window Keil Simulator 17-33 SPI Sample Code Keil Simulator 17-35 Serial Peripheral Interface SPI Keil Simulator 17-37 17.12 ∝Vision 2 Debug Program Example −17. Keil Debugger Serial Port I/O −18. Serial Channel 0 Communication Peripheral 17-42 BaudRate + fOSC @ Transmit Block Baud Rate ComputationBaudRate + fOSC Receive Block Baud Rate Computation −19. Clock Control Peripheral Additional Resource Appendix a Topic Additional Features in the MSC1210 Compared to Appendix B MSC1210 Timing Chain and Clock Control Diagram Figure B−1. MSC1210 Timing Chain and Clock Control Appendix C Table C−1. Boot ROM Routines Address Routine Declarations Description Boot ROM Routines Page Appendix D 8052 Instruction-Set Quick-Reference Guide JB bitAddr,relAddr Ajmp pg1Addr Appendix E Description Instruction Set Description Absolute Call within 2k Block 8052 Instruction SetAcall Acall codeAddress ADD A,operand ADD, AddcAdd Value, Add Value with Carry Ajmp codeAddress AjmpAbsolute Jump within 2k Block ANL operand1,operand2 ANLBitwise Clear Register Compare and Jump if Not EqualCLR Cjne operand1,operand2,reladdr Complement Register Decimal Adjust AccumulatorCPL CPL operand DEC register Decrementing the value causes it to reset to 255 0xFFHCarry flag is not set when the value rolls over from 0 to See also INC, Subb Decrement and Jump if Not Zero Djnz register,relAddr INC register INCIncrement Reister Jump if Bit Set and Clear Bit Jump if Bit SetJBC Jump if Carry Set JNC JMPJNB Ljmp JNZLcall MOV bit1,bit2 MOV operand1, operand2Not affected See also MOVC, MOVX, XCH, XCHD, PUSH, POP MOV operand1,operand2 MOVMove into/out of Internal RAM Movx MOV DptrMovc NOP MULMultiply Accumulator by B No Operation Syntax ORL operand1,operand2 ORLBitwise or Push POPPop Value from Stack Push Value onto Stack Reti RETReturn from Subroutine Return from Interrupt Setb RLCRRC Subb SjmpShort Jump Subtract from Accumulator with Borrow Xchd SwapXCH XRL Bitwise Exclusive or Undefined Instructions OpCode Bytes Cycles Flags ??? 0xA5 Appendix F EX2-External 2 Interrupt Enable Enable Interrupt Control EiconExtended Interrupt Enable EIE Bit Addressable SFRs alphabetical Interrupt Enable IE Extended Interrupt Priority EIP Interrupt Priority IP Port 0 P0 Port 1 P1 Port 2 P2 Port 3 P3 Program Status Word PSW Register Bank Register Bank Addresses Serial Mode Description Baud Serial Control Scon Timer Control Tcon Tcon Timer 2 Control T2CON T2CON Appendix G SFR/Address Cross-Reference SFR Name Description SFR Address Hex SFRs/Address Cross-Reference Guide alphabetical Spircon