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Texas Instruments MSC1210 manual Register Protection, Push PSW

Models: MSC1210

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Register Protection

10.10 Register Protection

One very important rule applies to all interrupt handlers: interrupts must leave the processor in the same state as it was in when the interrupt initiated. Re- member, the idea behind interrupts is that the main program is not aware that they are executing in the background. However, consider the following code:

CLR	C	;Clear carry
MOV	A,#25h	;Load the accumulator with 25h

ADDC A,#10h ;Add 10h, with carry

After the above three instructions are executed, the accumulator will contain a value of 35H.

However, what would happen if an interrupt occurred right after the MOV in- struction? During this interrupt, the carry bit was set and the value of the accu- mulator changed to 40H. When the interrupt finished and control was passed back to the main program, the ADDC would add 10H to 40H, and also add an additional 01H because the carry bit is set. The accumulator will contain the value 51H at the end of execution.

In this case, the main program has seemingly calculated the wrong answer. How can 25H + 10H yield 51H as a result? It does not make sense. A developer that was unfamiliar with interrupts would be convinced that the microcontroller was damaged in some way, provoking problems with mathematical calculations.

What has happened, in reality, is the interrupt did not protect the registers it used. Restated: an interrupt must leave the processor in the same state as it was in when the interrupt initiated.

This means if an interrupt uses the accumulator, it must insure that the value of the accumulator is the same at the end of the interrupt as it was at the begin- ning. This is generally accomplished with a PUSH and POP sequence at the beginning and end of each interrupt handler. For example:

INTERRUPT_HANDLER:
PUSH ACC	;Push the initial value of	accumulator
	;onto stack
PUSH PSW	;Push the initial value of	PSW SFR onto stack
MOV A,#0FFh	;Use accumulator & PSW for	whatever you want
ADD A,#02h	;Use accumulator & PSW for	whatever you want
POP PSW	;Restore the initial value of the PSW from
	;the stack
POP ACC	;Restore initial value of the accumulator
	;from stack

10-16

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Texas Instruments MSC1210 manual Register Protection, Push PSW

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 ConverterSerial Peripheral Interface SPI Additional MSC1210 HardwareAdditional Resource Boot ROM Routines Additional Features in the MSC1210 Compared toClock Timing Diagram Instruction-Set Quick-Reference GuideSPI/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 Description1 I/O Ports P0, P1, P2, and P3 AD7Port 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 TimingHigh 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 MSC1210Y5On-Chip Extended Static RAM Sram Data Memory−2. Program and Data Memory Addresses On-Chip Flash Data Memory External Data MemoryInternal RAM −2. MSC1210 Memory Map Register BankStack Register BanksBit Memory Or execute Special Function Register SFR Memory Defines the MSC1210 SFRs −1. SFR Names and Addresses SCON0Referencing SFRs Referencing Bits of SFRsBit−Addressable SFRs SFR TypesSFR 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 RegistersRegister Program Counter PCData Pointer DPTR0/DPTR1 Stack Pointer SPDescribes 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,AExternal Indirect Addressing Code Indirect AdressingDescribes the program flow of the MSC1210 ADC Conditional Branching Direct JumpsConsider 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 PsenDescribes 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 ModeCycle −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 TimerDetecting Timer Overflow Timing the Length of Events Using Timers as Event Counters Using Timer 1 T2CON SFRTimer 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 ModeSerial 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 * TH1Rcap 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 @ fOSCSerial Mode 3 Asynchronous Full-Duplex −7. Serial Port 0 Mode 3 Transmit TimingSetting 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 BaudBaud 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 SFRPolling Sequence −6.EIP F8 H SFR Interrupt Priorities−5.IP B8 H SFR Interrupt Triggering Exiting InterruptsExternal Interrupts Types of InterruptsSerial Interrupts −7.EXIF 91 H SFR Bit Name Explanation of FunctionAuxiliary 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/EventWaking Up from Idle Mode −13. EWU C6 H SFRRegister Protection Push PSWPush 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 WaveformsDuty 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 ExplanationsExample 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 Timing11-12 PGA DAC 12-10−1. MSC1210 Architecture −2. Input Multiplexer Configuration Input MultiplexerPositive Input Negative InputTemperature Sensor 12-6 Burnout Current Sources MSB@ 10 Input BufferAnalog Input ACLKFrequency−1.PGA Settings Programmable Gain Amplifier PGAOffset DAC ModulatorCalibration −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 FilterVoltage Reference −5.Output Data Rate and Channel Rate 10x fasterSummation/Shifter Register SourceSummation Count Shift Summation CountManual Summation Mode ADC Summation ModeManual Shift Divide Mode ADC Summation with Shift Divide ModeInterrupt-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 OUTDifferential 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 ClockSPI System Errors −3. SPI Reset State Data Transfers13-8 Fifo Operation −4. SPI Fifo OperationCode 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 ParametersWatchdog Timer Watchdog Timer Hardware ConfigurationEnabling Watchdog Timer Watchdog Timer Resetting the Watchdog Timer Disabling Watchdog Timer Watchdog Timeout/ActivationAdvanced Flash Memory 15-6 Hardware Configuration 15-2Power Optimization 15-9 Breakpoint Generator 15-7Hardware Configuration Hardware Configuration RegistersHardware Configuration Register 0 HCR0 DFSEL2/1/0 Amount of Flash Data MemoryHardware Configuration Register 1 HCR1 Hardware Configuration Memory Accessing Configuration Memory in a User ProgramWrite Protecting Flash Program Memory Updating Interrupts with Reset Sector LockAdvanced Flash Memory Configuring Breakpoints Breakpoint GeneratorBreakpoint Auxiliary Interrupt Disabling a BreakpointPower 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 OperatorChanging Program Flow LJMP, SJMP, Ajmp Ljmp LABEL3Subroutines LCALL, ACALL, RET Register Assignment MOV MOV DestinationRegister,SourceValueMOV 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 DebouncekeyLess Than and Greater Than Comparison Cjne Checkless JC AislessZero and Non-Zero Decisions JZ/JNZ Performing Additions ADD, AddcPerforming 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 XRLAssembly Language 16-25 Exchanging Register Values XCH Swapping Accumulator Nibbles SwapAdjusting 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 SUBSUB 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 − ModeTimer 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 ControlAnalog-to-Digital Converter −8. Analog−to−Digital Converter Peripheral −9. Error Message Summation/Shifter −10. Accumulator/Shifter Peripheral17.8.1 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 PortsSerial Peripheral Interface SPI −16. SPI Peripheral WindowKeil 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 TopicAdditional Features in the MSC1210 Compared to Appendix B MSC1210 Timing Chain and Clock Control Diagram Figure B−1. MSC1210 Timing Chain and Clock ControlAppendix C Table C−1. Boot ROM Routines Address Routine Declarations DescriptionBoot ROM Routines Page Appendix D 8052 Instruction-Set Quick-Reference Guide JB bitAddr,relAddr Ajmp pg1AddrAppendix E Description Instruction SetDescription Absolute Call within 2k Block 8052 Instruction SetAcall Acall codeAddressADD 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,reladdrComplement Register Decimal Adjust AccumulatorCPL CPL operandDEC 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, SubbDecrement and Jump if Not Zero Djnz register,relAddrINC register INCIncrement Reister Jump if Bit Set and Clear Bit Jump if Bit SetJBC Jump if Carry SetJNC 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 OperationSyntax ORL operand1,operand2 ORLBitwise or Push POPPop Value from Stack Push Value onto StackReti RETReturn from Subroutine Return from InterruptSetb RLCRRC Subb SjmpShort Jump Subtract from Accumulator with BorrowXchd SwapXCH XRL Bitwise Exclusive orUndefined Instructions OpCode Bytes Cycles Flags ??? 0xA5Appendix F EX2-External 2 Interrupt Enable Enable Interrupt Control EiconExtended Interrupt Enable EIE Bit Addressable SFRs alphabeticalInterrupt Enable IE Extended Interrupt Priority EIPInterrupt Priority IP Port 0 P0Port 1 P1 Port 2 P2Port 3 P3 Program Status Word PSW Register Bank Register Bank AddressesSerial Mode Description Baud Serial Control SconTimer Control Tcon TconTimer 2 Control T2CON T2CONAppendix G SFR/Address Cross-Reference SFR Name Description SFR Address HexSFRs/Address Cross-Reference Guide alphabetical Spircon