80C186EC/80C188EC Microprocessor User's Manual

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CHAPTER 12 WATCHDOG TIMER UNIT System upsets can come from a variety of sources. Errant software can work its way into an endless loop, waiting for an event that never occurs. An unanticipated radiation source can couple into improperly shielded circuitry. Not all sources of system upsets can be anticipated and guarded against. The Watchdog Timer Unit provides a graceful method for recovery from unexpected hardware and software upsets. Watchdog timers are designed to reset the system unless the timer is periodically reloaded with a new value (this is also known as “kicking the watchdog”). The system software is responsible for reloading the watchdog timer. It is assumed that errant code or a system lockup will prevent the watchdog timer from being reloaded, resulting in a system reset. A special instruction sequence, a sequence that errant code would be very unlikely to produce, is typically used to reload the timer. The Watchdog Timer Unit (WDT) can function either as a system watchdog or as a general-purpose timer, or it can be disabled for systems that do not wish to use it. 12.1 FUNCTIONAL OVERVIEW A block diagram of the Watchdog Timer Unit is shown in Figure 12-1. The 32-bit down counter decrements every CLKOUT cycle. The WDTOUT pin is driven low for four CLKOUT cycles when the down counter reaches zero (a WDT timeout). The WDTOUT signal may be used to reset the device or as an interrupt request. The down counter is reloaded with the 32-bit reload value under two conditions: • when a special LOCKed instruction sequence is issued to the Protection and Control Circuitry • when the down counter reaches zero The Protection and Control Circuitry is responsible for enabling and disabling the Watchdog Timer as well as preventing unauthorized modification of count values. 12.2 USING THE WATCHDOG TIMER AS A SYSTEM WATCHDOG There are two methods for recovery following a software upset: a full system reset or an interrupt request. Both methods can be implemented with the Watchdog Timer Unit. 12-1
WATCHDOG TIMER UNIT Figure 12-2 shows the circuit necessary to reset the processor when a WDT timeout occurs. The power-on reset signal and the WDTOUT signals are ANDed together to produce the RESIN signal for the processor. Internal Data Bus (F-BUS) Protection And Control Circuitry 32-BIT Reload Value 32-BIT Down Counter WDTOUT CLKOUT A1302-0A Figure 12-1. Block Diagram of the Watchdog Timer Unit Processor WDTOUT RESIN Power-On-Reset (Active Low) A1303-0A Figure 12-2. Watchdog Timer Reset Circuit The circuit in Figure 12-3(a) is used to interrupt the processor when a WDT timeout occurs. Since WDTOUT is normally high, the Interrupt Control Unit must be programmed for edge sensitivity to prevent continuous interrupts from occurring. 12-2
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80C186EC/80C188EC Microprocessor Us
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Information in this document is pro
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CONTENTS 2.3 INTERRUPTS AND EXCEPTI
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CONTENTS 6.4 PROGRAMMING...........
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CONTENTS CHAPTER 9 TIMER/COUNTER UN
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CONTENTS 11.4 SERIAL COMMUNICATIONS
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CONTENTS FIGURES Figure Page 2-1 Si
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CONTENTS FIGURES Figure Page 6-6 ST
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CONTENTS FIGURES Figure Page 11-18
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CONTENTS Table TABLES Page C-1 Inst
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Introduction 1
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INTRODUCTION The 80C186 Modular Cor
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INTRODUCTION Table 1-2. Related Doc
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INTRODUCTION 1.3.2.1 How to Find Ap
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Overview of the 80C186 Family Archi
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OVERVIEW OF THE 80C186 FAMILY ARCHI
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Bus Interface Unit 3
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BUS INTERFACE UNIT Physical Impleme
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BUS INTERFACE UNIT (X + 1) (X) A19:
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BUS INTERFACE UNIT For word transfe
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BUS INTERFACE UNIT CLKOUT T4 T1 T2
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BUS INTERFACE UNIT CLKOUT T4 or TI
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BUS INTERFACE UNIT Signals From CPU
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BUS INTERFACE UNIT T2 T3 or TW T4 o
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BUS INTERFACE UNIT A normally not-r
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BUS INTERFACE UNIT T2 or T3 or TW T
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BUS INTERFACE UNIT An idle bus stat
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BUS INTERFACE UNIT T1 T2 T3 T4 CLKO
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BUS INTERFACE UNIT T1 T2 T3 T4 CLKO
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BUS INTERFACE UNIT The minimum devi
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BUS INTERFACE UNIT Figure 3-24 show
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BUS INTERFACE UNIT After several TI
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BUS INTERFACE UNIT 3.5.5 Temporaril
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BUS INTERFACE UNIT CLKOUT ALE T4 T1
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BUS INTERFACE UNIT CLKOUT NMI/NTx N
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BUS INTERFACE UNIT ALE Processor A1
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BUS INTERFACE UNIT The WAIT instruc
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BUS INTERFACE UNIT CLKOUT HOLD 1 2
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BUS INTERFACE UNIT CLKOUT 1 3 4 HOL
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BUS INTERFACE UNIT CLKOUT HOLD 1 2
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Peripheral Control Block 4
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PERIPHERAL CONTROL BLOCK Register N
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PERIPHERAL CONTROL BLOCK 4.3 RESERV
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PERIPHERAL CONTROL BLOCK 4.4.3.1 Wr
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Clock Generation and Power Manageme
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CLOCK GENERATION AND POWER MANAGEME
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CHAPTER 6 CHIP-SELECT UNIT Every sy
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CHIP-SELECT UNIT Stop Value Ignore
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CHIP-SELECT UNIT Address 1 Ready Fl
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CHIP-SELECT UNIT Register Name: Reg
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CHIP-SELECT UNIT Register Name: Reg
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CHIP-SELECT UNIT In the previous eq
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CHIP-SELECT UNIT No Any READY = 1 W
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CHIP-SELECT UNIT The GCS chip-selec
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CHIP-SELECT UNIT $ TITLE (Chip-Sele
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CHIP-SELECT UNIT ;SET UP CHIP SELEC
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Refresh Control Unit 7
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REFRESH CONTROL UNIT 7.1 THE ROLE O
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REFRESH CONTROL UNIT The BIU does n
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REFRESH CONTROL UNIT CLKOUT T4 T1 T
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REFRESH CONTROL UNIT 7.7.2.1 Refres
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REFRESH CONTROL UNIT Register Name:
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REFRESH CONTROL UNIT $mod186 name e
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REFRESH CONTROL UNIT T1 T1 T1 T1 T1
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CHAPTER 8 INTERRUPT CONTROL UNIT Th
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INTERRUPT CONTROL UNIT Polling requ
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INTERRUPT CONTROL UNIT INT INTA D7:
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INTERRUPT CONTROL UNIT Edge Sense L
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INTERRUPT CONTROL UNIT 8.3.2 Interr
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INTERRUPT CONTROL UNIT 8.3.3.1 Defa
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INTERRUPT CONTROL UNIT More than on
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INTERRUPT CONTROL UNIT IR0 IR1 IR2
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INTERRUPT CONTROL UNIT 10. On the s
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INTERRUPT CONTROL UNIT 8.3.7 Altern
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INTERRUPT CONTROL UNIT 8.4.2 Progra
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INTERRUPT CONTROL UNIT Begin Initia
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INTERRUPT CONTROL UNIT 8.4.3.3 ICW2
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INTERRUPT CONTROL UNIT Register Nam
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INTERRUPT CONTROL UNIT Table 8-2. O
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INTERRUPT CONTROL UNIT The ESMM (En
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INTERRUPT CONTROL UNIT Internal Int
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INTERRUPT CONTROL UNIT To Slave 825
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INTERRUPT CONTROL UNIT 8.6.1 Interr
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INTERRUPT CONTROL UNIT CPU WR RD GC
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INTERRUPT CONTROL UNIT Non-Alike Ac
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INTERRUPT CONTROL UNIT ;Now start t
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INTERRUPT CONTROL UNIT ;The followi
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CHAPTER 9 TIMER/COUNTER UNIT The Ti
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TIMER/COUNTER UNIT Timer 0 Timer 1
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TIMER/COUNTER UNIT Continued From "
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TIMER/COUNTER UNIT Register Name: R
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TIMER/COUNTER UNIT The timer counti
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TIMER/COUNTER UNIT Timer 0 Serviced
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TIMER/COUNTER UNIT 9.3.2 Synchroniz
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TIMER/COUNTER UNIT lib_80186 segmen
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TIMER/COUNTER UNIT $mod186 name exa
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TIMER/COUNTER UNIT _CMPB equ word p
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CHAPTER 10 DIRECT MEMORY ACCESS UNI
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DIRECT MEMORY ACCESS UNIT 10.1.1.1
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DIRECT MEMORY ACCESS UNIT The Chip-
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DIRECT MEMORY ACCESS UNIT Both Requ
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DIRECT MEMORY ACCESS UNIT Channel a
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DIRECT MEMORY ACCESS UNIT Register
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Page 328: Serial Communications Unit 11
Page 331 and 332: SERIAL COMMUNICATIONS UNIT 1 2 3 4
Page 333 and 334: SERIAL COMMUNICATIONS UNIT The RX m
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Page 388 and 389: INPUT/OUTPUT PORTS Register Name: R
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Page 392: Math Coprocessing 14
Page 395 and 396: MATH COPROCESSING 14.3 THE 80C187 M
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APPENDIX A 80C186 INSTRUCTION SET A
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80C186 INSTRUCTION SET ADDITIONS AN
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Input Synchronization B
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INPUT SYNCHRONIZATION A synchroniza
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APPENDIX C INSTRUCTION SET DESCRIPT
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INSTRUCTION SET DESCRIPTIONS Table
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INSTRUCTION SET DESCRIPTIONS NEG NO
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INSTRUCTION SET DESCRIPTIONS SHR ST
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APPENDIX D INSTRUCTION SET OPCODES
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INSTRUCTION SET OPCODES AND CLOCK C
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Index
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INDEX AH register, 2-5 AL register,
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INDEX synchronization, 10-23 transf
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INDEX NMI, 2-42 generating with WDT
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INDEX bus latency, 7-7 calculating
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INDEX Trap exceptions, 2-42 Trap Fl
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80C186EC/80C188EC Microprocessor User's Manual

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