EECE 321L Lab Report, Spring 2008

 2001 Microchip Technology Inc. DS35007B PIC16F84A Data Sheet 18-pin Enhanced FLASH/EEPROM 8-bit Microcontroller M DS35007B - page ii  2001 Microchip Technology Inc. Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip’s products as critical com- ponents in life support systems is not authorized except with express written approval by Microchip. No licenses are con- veyed, implicitly or otherwise, under any intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, PIC, PICmicro, PICMASTER, PICSTART, PRO MATE, KEELOQ, SEEVAL, MPLAB and The Embedded Control Solutions Company are reg- istered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. Total Endurance, ICSP, In-Circuit Serial Programming, Filter- Lab, MXDEV, microID, FlexROM, fuzzyLAB, MPASM, MPLINK, MPLIB, PICC, PICDEM, PICDEM.net, ICEPIC, Migratable Memory, FanSense, ECONOMONITOR, Select Mode and microPort are trademarks of Microchip Technology Incorporated in the U.S.A. Serialized Quick Term Programming (SQTP) is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. © 2001, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. Microchip received QS-9000 quality system certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona in July 1999. The Company’s quality system processes and procedures are QS-9000 compliant for its PICmicro® 8-bit MCUs, KEELOQ® code hopping devices, Serial EEPROMs and microperipheral products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001 certified. Note the following details of the code protection feature on PICmicro® MCUs. • The PICmicro family meets the specifications contained in the Microchip Data Sheet. • Microchip believes that its family of PICmicro microcontrollers is one of the most secure products of its kind on the market today, when used in the intended manner and under normal conditions. • There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowl- edge, require using the PICmicro microcontroller in a manner outside the operating specifications contained in the data sheet. The person doing so may be engaged in theft of intellectual property. • Microchip is willing to work with the customer who is concerned about the integrity of their code. • Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable”. • Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our product. If you have any further questions about this matter, please contact the local sales office nearest to you.  2001 Microchip Technology Inc. DS35007B-page 1 M PIC16F84A High Performance RISC CPU Features: • Only 35 single word instructions to learn • All instructions single-cycle except for program branches which are two-cycle • Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle • 1024 words of program memory • 68 bytes of Data RAM • 64 bytes of Data EEPROM • 14-bit wide instruction words • 8-bit wide data bytes • 15 Special Function Hardware registers • Eight-level deep hardware stack • Direct, indirect and relative addressing modes • Four interrupt sources: - External RB0/INT pin - TMR0 timer overflow - PORTB<7:4> interrupt-on-change - Data EEPROM write complete Peripheral Features: • 13 I/O pins with individual direction control • High current sink/source for direct LED drive - 25 mA sink max. per pin - 25 mA source max. per pin • TMR0: 8-bit timer/counter with 8-bit programmable prescaler Special Microcontroller Features: • 10,000 erase/write cycles Enhanced FLASH Program memory typical • 10,000,000 typical erase/write cycles EEPROM Data memory typical • EEPROM Data Retention > 40 years • In-Circuit Serial Programming™ (ICSP™) - via two pins • Power-on Reset (POR), Power-up Timer (PWRT), Oscillator Start-up Timer (OST) • Watchdog Timer (WDT) with its own On-Chip RC Oscillator for reliable operation • Code protection • Power saving SLEEP mode • Selectable oscillator options Pin Diagrams CMOS Enhanced FLASH/EEPROM Technology: • Low power, high speed technology • Fully static design • Wide operating voltage range: - Commercial: 2.0V to 5.5V - Industrial: 2.0V to 5.5V • Low power consumption: - < 2 mA typical @ 5V, 4 MHz - 15 µA typical @ 2V, 32 kHz - < 0.5 µA typical standby current @ 2V RA1 RA0 OSC1/CLKIN OSC2/CLKOUT VDD RB7 RB6 RB5 RB4 RA2 RA3 RA4/T0CKI MCLR VSS RB0/INT RB1 RB2 RB3 •1 2 3 4 5 6 7 8 9 18 17 16 15 14 13 12 11 10 PDIP, SOIC PIC16F84A RA1 RA0 OSC1/CLKIN OSC2/CLKOUT VDD RB7 RB6 RB5 RB4 RA2 RA3 RA4/T0CKI MCLR VSS RB0/INT RB1 RB2 RB3 •1 2 3 4 5 6 7 8 9 20 19 18 17 16 15 14 13 12 SSOP PIC16F84A 10 11 VSS VDD 18-pin Enhanced FLASH/EEPROM 8-Bit Microcontroller PIC16F84A DS35007B-page 2  2001 Microchip Technology Inc. Table of Contents 1.0 Device Overview .......................................................................................................................................................................... 3 2.0 Memory Organization ................................................................................................................................................................... 5 3.0 Data EEPROM Memory ............................................................................................................................................................. 13 4.0 I/O Ports ..................................................................................................................................................................................... 15 5.0 Timer0 Module ........................................................................................................................................................................... 19 6.0 Special Features of the CPU...................................................................................................................................................... 21 7.0 Instruction Set Summary ............................................................................................................................................................ 35 8.0 Development Support................................................................................................................................................................. 43 9.0 Electrical Characteristics ............................................................................................................................................................ 49 10.0 DC/AC Characteristic Graphs .................................................................................................................................................... 61 11.0 Packaging Information................................................................................................................................................................ 71 Appendix A: Revision History .............................................................................................................................................................. 75 Appendix B: Conversion Considerations.............................................................................................................................................. 76 Appendix C: Migration from Baseline to Mid-Range Devices .............................................................................................................. 78 Index .................................................................................................................................................................................................... 79 On-Line Support................................................................................................................................................................................... 83 Reader Response ................................................................................................................................................................................ 84 PIC16F84A Product Identification System ........................................................................................................................................... 85 TO OUR VALUED CUSTOMERS It is our intention to provide our valued customers with the best documentation possible to ensure successful use of your Microchip products. To this end, we will continue to improve our publications to better suit your needs. Our publications will be refined and enhanced as new volumes and updates are introduced. If you have any questions or comments regarding this publication, please contact the Marketing Communications Department via E-mail at docerrors@mail.microchip.com or fax the Reader Response Form in the back of this data sheet to (480) 792-4150. We welcome your feedback. Most Current Data Sheet To obtain the most up-to-date version of this data sheet, please register at our Worldwide Web site at: http://www.microchip.com You can determine the version of a data sheet by examining its literature number found on the bottom outside corner of any page. The last character of the literature number is the version number, (e.g., DS30000A is version A of document DS30000). Errata An errata sheet, describing minor operational differences from the data sheet and recommended workarounds, may exist for current devices. As device/documentation issues become known to us, we will publish an errata sheet. The errata will specify the revision of silicon and revision of document to which it applies. To determine if an errata sheet exists for a particular device, please check with one of the following: • Microchip’s Worldwide Web site; http://www.microchip.com • Your local Microchip sales office (see last page) • The Microchip Corporate Literature Center; U.S. FAX: (480) 792-7277 When contacting a sales office or the literature center, please specify which device, revision of silicon and data sheet (include liter- ature number) you are using. Customer Notification System Register on our web site at www.microchip.com/cn to receive the most current information on all of our products.  2001 Microchip Technology Inc. DS35007B-page 3 PIC16F84A 1.0 DEVICE OVERVIEW This document contains device specific information for the operation of the PIC16F84A device. Additional information may be found in the PICmicro™ Mid- Range Reference Manual, (DS33023), which may be downloaded from the Microchip website. The Refer- ence Manual should be considered a complementary document to this data sheet, and is highly recom- mended reading for a better understanding of the device architecture and operation of the peripheral modules. The PIC16F84A belongs to the mid-range family of the PICmicro® microcontroller devices. A block diagram of the device is shown in Figure 1-1. The program memory contains 1K words, which trans- lates to 1024 instructions, since each 14-bit program memory word is the same width as each device instruc- tion. The data memory (RAM) contains 68 bytes. Data EEPROM is 64 bytes. There are also 13 I/O pins that are user-configured on a pin-to-pin basis. Some pins are multiplexed with other device functions. These functions include: • External interrupt • Change on PORTB interrupt • Timer0 clock input Table 1-1 details the pinout of the device with descrip- tions and details for each pin. FIGURE 1-1: PIC16F84A BLOCK DIAGRAM FLASH Program Memory Program Counter 13 Program Bus Instruction Register 8 Level Stack (13-bit) Direct Addr 8 Instruction Decode & Control Timing Generation OSC2/CLKOUT OSC1/CLKIN Power-up Timer Oscillator Start-up Timer Power-on Reset Watchdog Timer MCLR VDD, VSS W reg ALU MUX I/O Ports TMR0 STATUS reg FSR reg Indirect Addr RA3:RA0 RB7:RB1 RA4/T0CKI EEADR EEPROM Data Memory 64 x 8 EEDATA Addr Mux RAM Addr RAM File Registers EEPROM Data Memory Data Bus 5 7 7 RB0/INT 14 8 8 1K x 14 68 x 8 PIC16F84A DS35007B-page 4  2001 Microchip Technology Inc. TABLE 1-1: PIC16F84A PINOUT DESCRIPTION Pin Name PDIP No. SOIC No. SSOP No. I/O/P Type Buffer Type Description OSC1/CLKIN 16 16 18 I ST/CMOS(3) Oscillator crystal input/external clock source input. OSC2/CLKOUT 15 15 19 O — Oscillator crystal output. Connects to crystal or resonator in Crystal Oscillator mode. In RC mode, OSC2 pin outputs CLKOUT, which has 1/4 the frequency of OSC1 and denotes the instruction cycle rate. MCLR 4 4 4 I/P ST Master Clear (Reset) input/programming voltage input. This pin is an active low RESET to the device. PORTA is a bi-directional I/O port. RA0 17 17 19 I/O TTL RA1 18 18 20 I/O TTL RA2 1 1 1 I/O TTL RA3 2 2 2 I/O TTL RA4/T0CKI 3 3 3 I/O ST Can also be selected to be the clock input to the TMR0 timer/counter. Output is open drain type. PORTB is a bi-directional I/O port. PORTB can be software programmed for internal weak pull-up on all inputs. RB0/INT 6 6 7 I/O TTL/ST(1) RB0/INT can also be selected as an external interrupt pin. RB1 7 7 8 I/O TTL RB2 8 8 9 I/O TTL RB3 9 9 10 I/O TTL RB4 10 10 11 I/O TTL Interrupt-on-change pin. RB5 11 11 12 I/O TTL Interrupt-on-change pin. RB6 12 12 13 I/O TTL/ST(2) Interrupt-on-change pin. Serial programming clock. RB7 13 13 14 I/O TTL/ST(2) Interrupt-on-change pin. Serial programming data. VSS 5 5 5,6 P — Ground reference for logic and I/O pins. VDD 14 14 15,16 P — Positive supply for logic and I/O pins. Legend: I= input O = Output I/O = Input/Output P = Power — = Not used TTL = TTL input ST = Schmitt Trigger input Note 1: This buffer is a Schmitt Trigger input when configured as the external interrupt. 2: This buffer is a Schmitt Trigger input when used in Serial Programming mode. 3: This buffer is a Schmitt Trigger input when configured in RC oscillator mode and a CMOS input otherwise.  2001 Microchip Technology Inc. DS35007B-page 5 PIC16F84A 2.0 MEMORY ORGANIZATION There are two memory blocks in the PIC16F84A. These are the program memory and the data memory. Each block has its own bus, so that access to each block can occur during the same oscillator cycle. The data memory can further be broken down into the general purpose RAM and the Special Function Registers (SFRs). The operation of the SFRs that control the “core” are described here. The SFRs used to control the peripheral modules are described in the section discussing each individual peripheral module. The data memory area also contains the data EEPROM memory. This memory is not directly mapped into the data memory, but is indirectly mapped. That is, an indirect address pointer specifies the address of the data EEPROM memory to read/write. The 64 bytes of data EEPROM memory have the address range 0h-3Fh. More details on the EEPROM memory can be found in Section 3.0. Additional information on device memory may be found in the PICmicro™ Mid-Range Reference Manual, (DS33023). 2.1 Program Memory Organization The PIC16FXX has a 13-bit program counter capable of addressing an 8K x 14 program memory space. For the PIC16F84A, the first 1K x 14 (0000h-03FFh) are physically implemented (Figure 2-1). Accessing a loca- tion above the physically implemented address will cause a wraparound. For example, for locations 20h, 420h, 820h, C20h, 1020h, 1420h, 1820h, and 1C20h, the instruction will be the same. The RESET vector is at 0000h and the interrupt vector is at 0004h. FIGURE 2-1: PROGRAM MEMORY MAP AND STACK - PIC16F84A PC<12:0> Stack Level 1 • Stack Level 8 RESET Vector Peripheral Interrupt Vector •• User Memory Space CALL, RETURN RETFIE, RETLW 13 0000h 0004h 1FFFh 3FFh PIC16F84A DS35007B-page 6  2001 Microchip Technology Inc. 2.2 Data Memory Organization The data memory is partitioned into two areas. The first is the Special Function Registers (SFR) area, while the second is the General Purpose Registers (GPR) area. The SFRs control the operation of the device. Portions of data memory are banked. This is for both the SFR area and the GPR area. The GPR area is banked to allow greater than 116 bytes of general purpose RAM. The banked areas of the SFR are for the registers that control the peripheral functions. Banking requires the use of control bits for bank selection. These control bits are located in the STATUS Register. Figure 2-2 shows the data memory map organization. Instructions MOVWF and MOVF can move values from the W register to any location in the register file (“F”), and vice-versa. The entire data memory can be accessed either directly using the absolute address of each register file or indirectly through the File Select Register (FSR) (Section 2.5). Indirect addressing uses the present value of the RP0 bit for access into the banked areas of data memory. Data memory is partitioned into two banks which contain the general purpose registers and the special function registers. Bank 0 is selected by clearing the RP0 bit (STATUS<5>). Setting the RP0 bit selects Bank 1. Each Bank extends up to 7Fh (128 bytes). The first twelve locations of each Bank are reserved for the Special Function Registers. The remainder are Gen- eral Purpose Registers, implemented as static RAM. 2.2.1 GENERAL PURPOSE REGISTER FILE Each General Purpose Register (GPR) is 8-bits wide and is accessed either directly or indirectly through the FSR (Section 2.5). The GPR addresses in Bank 1 are mapped to addresses in Bank 0. As an example, addressing loca- tion 0Ch or 8Ch will access the same GPR. FIGURE 2-2: REGISTER FILE MAP - PIC16F84A File Address 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 7Fh 80h 81h 82h 83h 84h 85h 86h 87h 88h 89h 8Ah 8Bh 8Ch FFh Bank 0 Bank 1 Indirect addr.(1) Indirect addr.(1) TMR0 OPTION_REG PCL STATUS FSR PORTA PORTB EEDATA EEADR PCLATH INTCON 68 General Purpose Registers (SRAM) PCL STATUS FSR TRISA TRISB EECON1 EECON2(1) PCLATH INTCON Mapped in Bank 0 Unimplemented data memory location, read as ’0’. File Address Note 1: Not a physical register. CFh D0h 4Fh 50h (accesses) — —  2001 Microchip Technology Inc. DS35007B-page 7 PIC16F84A 2.3 Special Function Registers The Special Function Registers (Figure 2-2 and Table 2-1) are used by the CPU and Peripheral functions to control the device operation. These registers are static RAM. The special function registers can be classified into two sets, core and peripheral. Those associated with the core functions are described in this section. Those related to the operation of the peripheral features are described in the section for that specific feature. TABLE 2-1: SPECIAL FUNCTION REGISTER FILE SUMMARY Addr Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Value on Power-on RESET Details on page Bank 0 00h INDF Uses contents of FSR to address Data Memory (not a physical register) ---- ---- 11 01h TMR0 8-bit Real-Time Clock/Counter xxxx xxxx 20 02h PCL Low Order 8 bits of the Program Counter (PC) 0000 0000 11 03h STATUS(2) IRP RP1 RP0 TO PD Z DC C 0001 1xxx 8 04h FSR Indirect Data Memory Address Pointer 0 xxxx xxxx 11 05h PORTA(4) — — — RA4/T0CKI RA3 RA2 RA1 RA0 ---x xxxx 16 06h PORTB(5) RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0/INT xxxx xxxx 18 07h — Unimplemented location, read as '0' — — 08h EEDATA EEPROM Data Register xxxx xxxx 13,14 09h EEADR EEPROM Address Register xxxx xxxx 13,14 0Ah PCLATH — — — Write Buffer for upper 5 bits of the PC(1) ---0 0000 11 0Bh INTCON GIE EEIE T0IE INTE RBIE T0IF INTF RBIF 0000 000x 10 Bank 1 80h INDF Uses Contents of FSR to address Data Memory (not a physical register) ---- ---- 11 81h OPTION_REG RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0 1111 1111 9 82h PCL Low order 8 bits of Program Counter (PC) 0000 0000 11 83h STATUS (2) IRP RP1 RP0 TO PD Z DC C 0001 1xxx 8 84h FSR Indirect data memory address pointer 0 xxxx xxxx 11 85h TRISA — — — PORTA Data Direction Register ---1 1111 16 86h TRISB PORTB Data Direction Register 1111 1111 18 87h — Unimplemented location, read as '0' — — 88h EECON1 — — — EEIF WRERR WREN WR RD ---0 x000 13 89h EECON2 EEPROM Control Register 2 (not a physical register) ---- ---- 14 0Ah PCLATH — — — Write buffer for upper 5 bits of the PC(1) ---0 0000 11 0Bh INTCON GIE EEIE T0IE INTE RBIE T0IF INTF RBIF 0000 000x 10 Legend: x = unknown, u = unchanged. - = unimplemented, read as '0', q = value depends on condition Note 1: The upper byte of the program counter is not directly accessible. PCLATH is a slave register for PC<12:8>. The contents of PCLATH can be transferred to the upper byte of the program counter, but the contents of PC<12:8> are never trans- ferred to PCLATH. 2: The TO and PD status bits in the STATUS register are not affected by a MCLR Reset. 3: Other (non power-up) RESETS include: external RESET through MCLR and the Watchdog Timer Reset. 4: On any device RESET, these pins are configured as inputs. 5: This is the value that will be in the port output latch. PIC16F84A DS35007B-page 8  2001 Microchip Technology Inc. 2.3.1 STATUS REGISTER The STATUS register contains the arithmetic status of the ALU, the RESET status and the bank select bit for data memory. As with any register, the STATUS register can be the destination for any instruction. If the STATUS register is the destination for an instruction that affects the Z, DC or C bits, then the write to these three bits is disabled. These bits are set or cleared according to device logic. Furthermore, the TO and PD bits are not writable. Therefore, the result of an instruction with the STATUS register as destination may be different than intended. For example, CLRF STATUS will clear the upper three bits and set the Z bit. This leaves the STATUS register as 000u u1uu (where u = unchanged). Only the BCF, BSF, SWAPF and MOVWF instructions should be used to alter the STATUS register (Table 7-2), because these instructions do not affect any status bit. REGISTER 2-1: STATUS REGISTER (ADDRESS 03h, 83h) Note 1: The IRP and RP1 bits (STATUS<7:6>) are not used by the PIC16F84A and should be programmed as cleared. Use of these bits as general purpose R/W bits is NOT recommended, since this may affect upward compatibility with future products. 2: The C and DC bits operate as a borrow and digit borrow out bit, respectively, in subtraction. See the SUBLW and SUBWF instructions for examples. 3: When the STATUS register is the destination for an instruction that affects the Z, DC or C bits, then the write to these three bits is disabled. The specified bit(s) will be updated according to device logic R/W-0 R/W-0 R/W-0 R-1 R-1 R/W-x R/W-x R/W-x IRP RP1 RP0 TO PD Z DC C bit 7 bit 0 bit 7-6 Unimplemented: Maintain as ‘0’ bit 5 RP0: Register Bank Select bits (used for direct addressing) 01 = Bank 1 (80h - FFh) 00 = Bank 0 (00h - 7Fh) bit 4 TO: Time-out bit 1 = After power-up, CLRWDT instruction, or SLEEP instruction 0 = A WDT time-out occurred bit 3 PD: Power-down bit 1 = After power-up or by the CLRWDT instruction 0 = By execution of the SLEEP instruction bit 2 Z: Zero bit 1 = The result of an arithmetic or logic operation is zero 0 = The result of an arithmetic or logic operation is not zero bit 1 DC: Digit carry/borrow bit (ADDWF, ADDLW,SUBLW,SUBWF instructions) (for borrow, the polarity is reversed) 1 = A carry-out from the 4th low order bit of the result occurred 0 = No carry-out from the 4th low order bit of the result bit 0 C: Carry/borrow bit (ADDWF, ADDLW,SUBLW,SUBWF instructions) (for borrow, the polarity is reversed) 1 = A carry-out from the Most Significant bit of the result occurred 0 = No carry-out from the Most Significant bit of the result occurred Note: A subtraction is executed by adding the two’s complement of the second operand. For rotate (RRF, RLF) instructions, this bit is loaded with either the high or low order bit of the source register. Legend: R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’ - n = Value at POR ’1’ = Bit is set ’0’ = Bit is cleared x = Bit is unknown  2001 Microchip Technology Inc. DS35007B-page 9 PIC16F84A 2.3.2 OPTION REGISTER The OPTION register is a readable and writable register which contains various control bits to configure the TMR0/WDT prescaler, the external INT interrupt, TMR0, and the weak pull-ups on PORTB. REGISTER 2-2: OPTION REGISTER (ADDRESS 81h) Note: When the prescaler is assigned to the WDT (PSA = ’1’), TMR0 has a 1:1 prescaler assignment. R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0 bit 7 bit 0 bit 7 RBPU: PORTB Pull-up Enable bit 1 = PORTB pull-ups are disabled 0 = PORTB pull-ups are enabled by individual port latch values bit 6 INTEDG: Interrupt Edge Select bit 1 = Interrupt on rising edge of RB0/INT pin 0 = Interrupt on falling edge of RB0/INT pin bit 5 T0CS: TMR0 Clock Source Select bit 1 = Transition on RA4/T0CKI pin 0 = Internal instruction cycle clock (CLKOUT) bit 4 T0SE: TMR0 Source Edge Select bit 1 = Increment on high-to-low transition on RA4/T0CKI pin 0 = Increment on low-to-high transition on RA4/T0CKI pin bit 3 PSA: Prescaler Assignment bit 1 = Prescaler is assigned to the WDT 0 = Prescaler is assigned to the Timer0 module bit 2-0 PS2:PS0: Prescaler Rate Select bits Legend: R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’ - n = Value at POR ’1’ = Bit is set ’0’ = Bit is cleared x = Bit is unknown 000 001 010 011 100 101 110 111 1 : 2 1 : 4 1 : 8 1 : 16 1 : 32 1 : 64 1 : 128 1 : 256 1 : 1 1 : 2 1 : 4 1 : 8 1 : 16 1 : 32 1 : 64 1 : 128 Bit Value TMR0 Rate WDT Rate PIC16F84A DS35007B-page 10  2001 Microchip Technology Inc. 2.3.3 INTCON REGISTER The INTCON register is a readable and writable register that contains the various enable bits for all interrupt sources. REGISTER 2-3: INTCON REGISTER (ADDRESS 0Bh, 8Bh) Note: Interrupt flag bits are set when an interrupt condition occurs, regardless of the state of its corresponding enable bit or the global enable bit, GIE (INTCON<7>). R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-x GIE EEIE T0IE INTE RBIE T0IF INTF RBIF bit 7 bit 0 bit 7 GIE: Global Interrupt Enable bit 1 = Enables all unmasked interrupts 0 = Disables all interrupts bit 6 EEIE: EE Write Complete Interrupt Enable bit 1 = Enables the EE Write Complete interrupts 0 = Disables the EE Write Complete interrupt bit 5 T0IE: TMR0 Overflow Interrupt Enable bit 1 = Enables the TMR0 interrupt 0 = Disables the TMR0 interrupt bit 4 INTE: RB0/INT External Interrupt Enable bit 1 = Enables the RB0/INT external interrupt 0 = Disables the RB0/INT external interrupt bit 3 RBIE: RB Port Change Interrupt Enable bit 1 = Enables the RB port change interrupt 0 = Disables the RB port change interrupt bit 2 T0IF: TMR0 Overflow Interrupt Flag bit 1 = TMR0 register has overflowed (must be cleared in software) 0 = TMR0 register did not overflow bit 1 INTF: RB0/INT External Interrupt Flag bit 1 = The RB0/INT external interrupt occurred (must be cleared in software) 0 = The RB0/INT external interrupt did not occur bit 0 RBIF: RB Port Change Interrupt Flag bit 1 = At least one of the RB7:RB4 pins changed state (must be cleared in software) 0 = None of the RB7:RB4 pins have changed state Legend: R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’ - n = Value at POR ’1’ = Bit is set ’0’ = Bit is cleared x = Bit is unknown  2001 Microchip Technology Inc. DS35007B-page 11 PIC16F84A 2.4 PCL and PCLATH The program counter (PC) specifies the address of the instruction to fetch for execution. The PC is 13 bits wide. The low byte is called the PCL register. This reg- ister is readable and writable. The high byte is called the PCH register. This register contains the PC<12:8> bits and is not directly readable or writable. If the pro- gram counter (PC) is modified or a conditional test is true, the instruction requires two cycles. The second cycle is executed as a NOP. All updates to the PCH reg- ister go through the PCLATH register. 2.4.1 STACK The stack allows a combination of up to 8 program calls and interrupts to occur. The stack contains the return address from this branch in program execution. Mid-range devices have an 8 level deep x 13-bit wide hardware stack. The stack space is not part of either program or data space and the stack pointer is not readable or writable. The PC is PUSHed onto the stack when a CALL instruction is executed or an interrupt causes a branch. The stack is POPed in the event of a RETURN, RETLW or a RETFIE instruction execution. PCLATH is not modified when the stack is PUSHed or POPed. After the stack has been PUSHed eight times, the ninth push overwrites the value that was stored from the first push. The tenth push overwrites the second push (and so on). 2.5 Indirect Addressing; INDF and FSR Registers The INDF register is not a physical register. Addressing INDF actually addresses the register whose address is contained in the FSR register (FSR is a pointer). This is indirect addressing. EXAMPLE 2-1: INDIRECT ADDRESSING Reading INDF itself indirectly (FSR = 0) will produce 00h. Writing to the INDF register indirectly results in a no-operation (although STATUS bits may be affected). A simple program to clear RAM locations 20h-2Fh using indirect addressing is shown in Example 2-2. EXAMPLE 2-2: HOW TO CLEAR RAM USING INDIRECT ADDRESSING An effective 9-bit address is obtained by concatenating the 8-bit FS