End
This is a directive, placed at the end of of program to tell the assembler to finish the job of assembling the instructions into .hex code. The directive is:

end

End of Table
The end of a table can be detected in two different ways.
If a value such as FF is not used in any of the data, it can be used as an End of Table marker. The sub-routine calling the table must look for 0FFh to detect End of Table.

Table

ADDWF 02h,1
RETLW 3Fh
RETLW 06h
RETLW 5Bh
RETLW 4Fh
RETLW 66h
RETLW 6Dh
RETLW 7Dh
RETLW 07h
RETLW 7Fh
RETLW 6Fh
RETLW 0FFh ;Add W to the Program Counter to create a jump.
;0    format= gfedcba
;1
;2
;3
;4
;5
;6
;7
;8
;9
;End of table marker

The other method is to count the number of items in a table and make sure the sub-routine calling the table doe not CALL values beyond this value.

Equal
To detect if two files are equal, they are XORed together. See XOR.

Equates   "equ"    you can also use "="
Equates assign an easy to remember label to a numeric value. This value can be a file or bit in a file.
e.g:
delay1 equ   20h    ;every time "delay1" is inserted into a program, the assembler will assign file 20h.

in your program:

   movlw   80h
   movwf   delay1       ;the assembler will put 80h into file 20h

The in/out pins on a 12F629 are 2,3,4,5,6 and 7.
These are GP5, GP4, GP3, GP2, GP1 and GP0
These correspond to GPIO,5 GPIO,4 GPIO,3 GPIO,2 GPIO,1 and GPIO,0 in a program.
Suppose GPIO,3 is called "switch"   and GPIO,5 is called "LED" (it drives a red LED).
In the equates section of your program (at the top of your program) you can equate bit "3" of the GPIO file as "switch and bit "5" as "LED."

The equates will appear as:

switch    equ   3    or    switch =   3
LED       equ   5    or    LED     =   5

in your program:

   btfss   GPIO,switch
or
   bsf     GPIO,LED

Error Message 302
If you get an error message when MPASM is compiling your program to a .hex file, it will not produce the .hex file.
To find the error messages, open the .lst file.
Some error messages are just a warning such as:

Message[302] myfile.ASM 136 :
Register in operand not in bank 0.  Ensure that bank bits are correct.

The above is a warning that you need to select the correct bank.
You can remove the warning message by inserting the following at the top of your .asm program

ERRORLEVEL -302     ;remove messages

Field
Your assembly program must be laid out in columns so the assembler can detect the instructions.

Label Field
must start a-z
or _2set
Mnemonic Field
(the instructions)
movlw
movwf Operand field

33h (hexidecimal)
or   0.26(digital 26) Comment Field
; starts with semicolon
(the assembler ignores all comments)

_3times movlw
movwf .45                                 ;forty-five
delay1                            ;this is the delay register

File Value (comparison)
Detecting the value of a file or register.

movlw
subwf,0

btfss 03,2

goto xxxx
goto yyyy ;load a value into w (say 8C)
;subtract 8C from w to see if the result is zero (store ;the result in w so that the file is not altered.
;test the zero bit in file 03 (status).
;It will be set if value=file
;value in w is not = value in file
;value in w = value in file

FSR See Indirect Addressing
This is a special file called File Select Register. It has the address 04. It is not a file like the other files in the micro but a POINTER FILE and is used in conjunction with another file called INDF.
INDF has the address 00.
INDF is not actually a file but a robot arm. It grabs the contents (or delivers contents) to a file pointed to by FSR. These are two special files (devices) that allow very powerful (low instruction) programming to be produced.
For instance, if FSR is loaded with 2C, it will tell INDF to grab (or deliver) contents to file 2C.
To do this, we need the instructions:
MOVLW 2C
MOVF 04
If we now put 8Fh into INDF, the value will actually go into file 2C.
This is called INDIRECT ADDRESSING.

GOTO
The GOTO instruction causes the micro to go to the address identified by a label such as "No" or "Yes."

No
Yes BTFSS GPIO,0
GOTO No
GOTO Yes
RETLW 00
MOVLW 3Fh
etc ;Is button pressed?
;No
;Yes

The instruction: goto $ + 2

"$" means the current address.

"+ 2" means to advance two instructions down the program.

btfss GPIO,0
goto $ + 2
instruction x
instruction y
instruction z
;this will end the micro to instruction y

;the micro will advance to this instruction
;the micro will never execute this instruction!!!!

To go "up" the program, the goto instruction is:
goto $ –3
or
goto $ –0dh
or     $ –.16   (minus decimal sixteen). The instruction should be written without any gaps: $–.16

When writing a program, you must make sure the micro will get back to the "Main" routine.
If you use a "call" instructions such as:

    call   delay_1

make sure the sub-routine has:

    retlw   00

to get the micro back to "Main."

You cannot use the instruction:

    goto   delay_1

as the "retlw   00" in the delay_1 routine will not take the micro back to "Main" as the return address has not been remembered with a "goto" instruction.

You can also define a location by writing the LABEL (in this case "Step") and an offset - in this case +1. The micro will go to "movwf tmr2." This has an advantage. It is easy to see, rather than writing $–4, when a large number of instructions are to be counted.

Step

movlw     25
movwf     tmr2
btfsc       Sw2
goto       newpress
decfsz   Sw2,f
goto      Step+1
retlw      00

Halt
Do not use the word "Halt" as a label, the assembler does not like it. Use Loop, Pause, Stop, Wait. See Loop and Stop.

To create a "halt" instruction:

Loop goto $ This will cause the microcontroller to keep looping the same instruction.

Halve (Half)
To halve (half - divide by two) the value of the contents of a file, it is shifted RIGHT (RRF 1A,1). The number must be an even number (it cannot have a bit in bit0).

HEX: see Decimal to Binary to HEX

Hex, Binary and Decimal numbers
Any mixture of binary, Hex and decimal numbers can be shown in a program.
Binary numbers are presented as: 0b'00000000' or b'00000000' or B'00000000' or 00000000b or b'0100' to indicate the lowest 4 bits.
Hex numbers are shown as: 0x2 or 0x0F (= fifteen) or 0x3C or h' or $ ($F or $f or $3A or $0ff )
or <digits>h (must begin with 0 ....9) examples: 80h 3Ah 0FFh or 0ffh (do not put ffh or FFh as the compiler requires 0 to 9 at beginning)
Decimal numbers are shown as: d'250' or decimal numbers without a prefix. They can also be written with a decimal point. examples: .250 .80 .100

Higher
To find out if a number is higher than a know value, a comparison is made. See Comparison.

Increment
To increment a file, use the instruction: INCF 2A,1. This puts the new value back into the file.
Using INCF 2A,0 puts the new value also into W!
To add two to a file, it can be incremented twice:
INCF 2A,1
INCF 2A,1
To double the value of a file, the contents is shifted left:
RLF 2A,1
A file can be incremented until it "rolls over to zero." Normally a file is decremented to zero and a skip occurs when it is zero. But the same effect can be produced by incrementing a file:
INCFSZ, 2A,1
To increment W, use ADDLW, thus: ADDLW 01 or ADDLW 3Bh

IOR - inclusive OR

Turn ON 2 or more outputs with IOR

The PIC12F629 does not like:

   bsf   GPIO, 0
   bsf   GPIO, 2

gpio,2 will not turn ON.

To turn ON, say gpio,0 gpio,1 and gpio,2 at the same time, use the following:
You do not need to know the state of the other outputs, and they will not be altered.

   movlw    b'00000111'
   iorwf       gpio,1

the result: gpio,0 gpio,1 and gpio,2   will be "set" (go to "1" - high) and gpio,3 gpio,4 gpio,5 will not be affected.

The same can be done to turn OFF 3 outputs:

   movlw    b'00000000'
   iorwf       gpio,1

result: gpio,0 gpio,1 and gpio,2   will be "clear" (go to "0" - low) and gpio,3 gpio,4 gpio,5 will not be affected.   This is NOT the same as: clrf    gpio

Indirect Addressing
A number of files can be addressed by a sub-routine and the information can be moved into each file or read from each file. The files must be a group.
Suppose we have 8 files and need to read the contents and output it to a display.
The files are: 21h, 22h, 23h, 24h, 25h, 26h, 27h, and 28h.
There are two special files that allow a sub-routine to be created to look at the 8 files and read the contents.
They are: INDF and FSR
The INDF file is not a real file. It is like a Robot Arm. It reaches down the list of files and picks up the contents or delivers the contents of a file to the programmer. The file it reaches is determined by the value in FSR.
FSR is loaded with the address of the file you wish to read or write.
This arrangement has an advantage. By loading FSR with a value, you can reach a file and by incrementing FSR, you can reach the next file etc.
If you load a value into INDF, you will actually load the value into the file pointed to by FSR.
If you read INDF, you will actually read the contents of the file pointed to by FSR.
You can consecutively read 8, 10 or 20 files or clear 20 files or load into 20 or more files with a simple looping sub-routine. It's a very powerful feature.
The following instructions put a value of 8Fh into file 21h.

MOVLW 21h
MOVWF 04
MOVLW 8Fh
MOVWF 00

;Load W with start of 8 files
;Load 21h into FSR
;Put 8F into W
;Put 8Fh into file 21h

The animation below shows how the information passes to the files:

Using INDF and FSR

The following instructions put a value of 8Fh into files 21h, 22h, 23h, 24h, 25h, 26h, 27h and 28h.

Loop1 MOVLW 08
MOVWF 20h
MOVLW 21h
MOVWF 04
MOVLW 8Fh
MOVWF 00
INCF 04
DECFSZ 20h
GOTO Loop1
RETURN ;8 loops of the program
;File 20h is the decrementing file
;Load W with start of 8 files
;Load 21h into FSR
;Put 8F into W
;Put 8Fh into file 21h
;Increment FSR to make INDF go to next file

The following instructions read files 21h, 22h, 23h, 24h, 25h, 26h, 27h and 28h and outputs to GPIO (file 05). Output Port 05 has only 5 lines: GP0, GP1, GP2, GP4 and GP5. GP3 is missing and this makes it difficult to display values from a file.

Loop1
MOVLW 08
MOVWF 20h
MOVLW 21h
MOVWF 04
MOVF 00,0
MOVWF GPIO
CALL Delay
INCF 04
DECFSZ 20h
GOTO Loop1
RETURN ;8 loops of the program
;File 20h is the decrementing file
;Load W with start of 8 files
;Load 21h into FSR
;Copy file 21h (or next file) into W
;Move W to output Port GPIO
;Show value LEDs etc
;Increment FSR to make INDF go to next file

INDF See Indirect Addressing and FSR
This is a special file called INDirect File.
INDF has the address 00.
INDF is not actually a file but a robot arm. It grabs the contents (or delivers contents) to a file pointed to by FSR.
This is used in an operation called INDIRECT ADDRESSING.

Input
The six bits of the in/out port GPIO can be made input or output by the value of the bits in a file called TRISIO. GP3 can only be INPUT.
To make a line INPUT, the corresponding TRISIO bit must be "1."
To make a line OUTPUT, the corresponding TRISIO bit must be "0."
To make a line INPUT (or OUTPUT), the instructions must be placed inside BSF 03,5 and BCF 03,5.
For example, to make the lowest line of GPIO, an INPUT, the following instructions are needed:

BSF 03,5
MOVLW 01
MOVWF GPIO
BCF 03,5 ;Go to Bank 1
;Load W with 0000 0001
;Make GP0 input
;Go to Bank 0 - the program memory area.

The other individual lines are:
movlw 02         ;Load W with 0000 0010
movwf GPIO   ;Make GP1 input

movlw 04         ;Load W with 0000 0100
movwf GPIO ;Make GP2 input

movlw 08         ;Load W with 0000 1000
movwf GPIO    ;Make GP3 input

movlw 10h       ;Load W with 0001 0000
movwf GPIO   ;Make GP4 input

movlw 20h       ;Load W with 0010 0000
movwf GPIO    ;Make GP5 input

To make more than one line (with a single instruction) an input, the hex values are added.

movlw 0F        ;Load W with 0000 1111
movwf GPIO ;Make GP0, GP1, GP2, GP3 input

movlw 12h       ;Load W with 0001 0010
movwf GPIO ;Make GP1, GP4 input

movlw 33h       ;Load W with 0011 0011
movwf GPIO    ;Make GP0, GP1, GP4, GP5 input

Port direction can be changed at any time during the running of a program. You must make sure that any input or output devices on the line will not upset the running of the program.
In this case it is best to SET or CLEAR a BIT. This involves setting or clearing an individual bit. This prevents touching any other lines.
Eg: To make the lowest line of port B an input:

bsf 03,5
bsf GPIO,0
bsf 03,5 ;Go to Bank 1
;Make GP0 input
;Go to Bank 0 - the program memory area.

Carry out instructions using the input line, then make the line an output:

bsf 03,5
bsf GPIO,0
bsf 03,5 ;Go to Bank 1
;Make GP0 output
;Go to Bank 0 - the program memory area.

Int   Integer
The abbreviation:
int   n_bytes    or   int nEmpty etc means integer.
An integer is a whole number, such as:   2, 346,   -458, but 1.5 is not an integer.
You will also find INT used in a program to refer to INTerrupt, or INTCON.

Interrupt
This program Loops until input GPIO,0 changes state. The micro then goes to address 4, then to Interrupt sub-routine where it changes the state of a LED connected to GPIO,0. It then clears the GPIF flag and returns to Main where it Loops.

Interrupt

Main

Loop

Org 0x00
Goto Main

Org 0x04
Goto   Interrupt

btfss   Interrupt,gpif
retfie
movlw b'00000001'
xorwf gpio,0
bcf    intcon,gpif
retfie

bsf   status,rp0
movlw b'00000001'
movwf trisio
bcf   status,rp0
movlw b'00001000'
movwf   intcon
bsf intcon,gie
nop
goto Loop ;Go to Bank 1
;Make GP0 output
;Go to Bank 0 - the program memory area.

;test if gpio,0 changed state
;return to Main

;blink LED
;clear gpif flag
;return to Main

;make gpio,0 input

;enable port-change interrupt

;enable all interrupts - bit7
;loops HERE until interrupt occurs

Jump
There is no "jump" instruction, however the "jump command" is included in instructions such as
decfsz, btfsc, with the actual instruction meaning to skip or "jump over" the next instruction if the file is not zero, or the bit is not clear.
The closest instruction is: "goto"

Normally the micro advances down the program, one instruction at a time and reads each instruction as it comes to it. If you want to jump down a program, you can add a number (literal) to the Program Counter and the micro will carry out the command.
The instruction is:
   addwf pcl,1
Suppose you need to go to one of 5 different sub-routines. This is done by placing a value in "w:"
movlw 01,   or movlw 02,   movlw 03,   movlw 04,   movlw 05
then the instruction: addwf pcl,1

To prevent a jump beyond the 5 "goto's, the instruction:    andlw 05h   is added here.

The next instructions will be:

nop                  ;this instruction is equal to: "movlw 00"
goto   sub-1
goto   sub-2
goto   sub-3
goto   sub-4
goto   sub-5

Label
This is the name given to each sub-routine. It is placed in the first column of your program (called an assembly program).
Some names cannot be used as they are reserved by the assembler. Keep the length to less than 8 letters. Do not use "-" or "/" Use "_" to separate.
Here are some examples:
Alarm Alarm_1 Beep Button Count Dec Delay Display Fast Find Flow Halt HeeHaw Inc Look Loop Main Send Show Siren Sound Sw Switch Table Table2 Table_3 Test Try Try_2 Toggle Tone Unit

Layout
Your assembly program must be laid out in columns so the assembler can detect the instructions.

Label Field
must start a-z
or _2set
Mnemonic Field
(the instructions)
movlw
movwf Operand field

33h (hexidecimal)
or   0.26(digital 26) Comment Field
; starts with semicolon
(the assembler ignores all comments)

_3times movlw
movwf .45                                 ;forty-five
delay1                            ;this is the delay register

Less than - see Comparison

Load a file
This operation cannot be done directly. A number (a value) is called a LITERAL. It is loaded into W then the value in W is moved to a file. The two instructions are:

MOVLW 0FFh
MOVWF 2A ;Load a value (called a Literal) (00 to 0FFh) into W
;Move the value in W to a file

Look at an Input
There is no instruction called "look." If a switch or button is connected to an input line such as the lowest line on GPIO, the instruction is:

BTFSS GPIO,0
GOTO No
GOTO Yes ;Is button pressed?
;No
;Yes

This assumes the switch is connected to the positive rail and the input goes HIGH when the button is pressed.
This instruction also works for a signal on line GPIO,1. You must make sure line GPIO,1 is an INPUT via the SetUp routine.
The two instructions after BTFSS GPIO,1 can be "GOTO Yes", "GOTO No" by changing the first instruction. The decision will depend on the number of instructions for the "Yes" or "No" answer, as the instruction placed directly after BTFSS GPIO,1 must be a GOTO.

BTFSC GPIO,1
GOTO Yes
GOTO No ;Is button pressed?
;Yes
;No

Loop
The action of looping is carried out for a number of reasons. The micro does not have a Halt or Stop feature and must carry out instructions at all times. A loop will hold the micro in one place.
To get out, a set of instructions such as "look" is needed inside the loop. These instructions see if a button has been pressed etc. Alternatively, if the watchdog timer is SET, the micro will come out of the loop and go to location 04. The instructions to create a loop are as follows:

Loop
NOP
GOTO Loop

To create a "loop" instruction:

Loop goto $ This will cause the microcontroller to keep looping the same instruction.

Lower
To find out if a number is lower than a know value, a comparison is made. See Comparison.

Macro
A Macro is similar to a sub-routine. You can call it from anywhere in a program. The aim of a macro is to save lines of code.

Some assemblers have built-in macros and recognise abbreviations such as the following:
Do not use these instructions unless you know EXACTLY what you are doing.
fr = file register
For instance, we will explain the following instruction in the table below:

Branch on No Zero to addr     =   btfss 3, 2    goto addr.   (file 3, bit 2 is the zero flag)
Test the zero flag. Skip if it is set. In other words skip if the zero flag is set, but BRANCH if it is not zero!
The normal instructions are as follows:
    btfss 3,2
    goto   tune1
    next instruction

alternately, you can use:
    bnz tune1
    next instruction

Mnemonic
addcf fr, d
subcf fr, d
negf fr, d
b   addr
bz   addr
bnz   addr
bc   addr
bnc   addr
skpc
skpnc
skpz
skpnz
clrz
setz
clrc
setc
tstf   fr
decbnz fr,addr

Description
Add carry to fr
Subtract carry from fr
Negate file register fr
Branch to addr
Branch on Zero to addr
Branch on No Zero to addr
Branch on Carry to addr
Branch on No Carry to addr
Skip on Carry
Skip on No Carry
Skip on Zero
Skip on No Zero
Clear Zero flag
Set Zero flag
Clear Carry flag
Set Carry flag
Test file register fr
Decrement fr, if zero branch to addr

Function
btfsc 3, 0 incf f,d
btfsc 3, 0 decf fr,d
comf fr, 1 incf fr,d
goto    adddr
btfsc 3, 2    goto addr
btfss 3, 2    goto addr
btfsc 3, 0    goto addr
btfss 3, 0    goto addr
btfss 3, 0
btfsc 3, 0
btfss 3, 2
btfsc 3, 2
bcf    3, 2
bsf    3, 2
bcf    3, 0
bsf    3, 0
movf  fr, f
decfsz  fr goto addr

A macro can be created to move a number (a literal) into a file, using a single instruction. This normally requires two instructions:
    movlw 64h     ;put 64h into W
    movwf 2Ch    ;move 64h to file 2C

The single instruction we will create is:

   movlf 64h,2Ch ;this instruction will put 64h into file 2C. (a macro must be included in the program)

To create a macro for the instruction "movlf"    the following is placed at the top of your program:

movlf   macro literal,file    ;literal -> file
          movlw literal
          movwf file
          endm

When you write the instruction: movlf 4Ah,2Fh     ;4A will be placed into file 2F.

Main
The Main routine is constantly looped and generally consists of sub-routines that are CALLed.

Main

CALL Switch
CALL Display
CALL Beep
GOTO Main

;Loop Main

Mask - see also AND for a "2-instruction" code
If you want to remove a number of bits from a file, the operation is called MASKING.
You can remove the high or low nibble (a nibble is a set of 4 bits) or any other bits. Any number from 0 - 7 can be obtained by masking (removing) bits 3,4,5,6,7, and leaving only bits 0, 1 and 2.
To mask (remove) the upper nibble, the number is ANDed with 0F. To mask the lower nibble, the number is ANDed with F0. (this is written: 0F0h in the program)

number:
W:
answer:

1001 0111
1111 0000
1001 0000

MOVLW 97h
MOVWF 2A
MOVLW 0F0h
ANDWF 2A,1

;Put 97h into W
;Move 97h into file 2A
;put the "masking value" into W
;AND 97h with file 2A. The result will be in file 2A.

More than - see Comparison

Move a file to W
The contents of a file can be moved to W with the following instruction:
MOVF 2A,0 The contents are actually COPIED. The original file still holds the contents.

Move a file to another file
The contents of a file can be moved to another file via the following instructions.
It is firstly copied to W then W is copied to the new file:

MOVF 2A,0
MOVWF 2B ;The contents of file 2A is copied to W
;W is copied to file 2B

Multiply
Simple multiplication such as multiply by 2 can be performed by the RLF instruction. Successive RLF's will multiply by 4, 8, sixteen etc. You need to be careful as this is called a "blind" operation.
A number such as 80h (128) will not be doubled as 1000 0000 will be moved to the left and the top bit will be passed to the Carry. Only numbers up to 7F (127) can be doubled.
To multiply by 2:

RLF 2A,1 ;The contents of file 2A is doubled

To multiply any two numbers together requires a program. Since the PIC12F629 does not have any multiply function, it is carried out by successive ADDITIONS. A number from 01 to 255 can be multiplied by 01 to 255.
To multiply 75(4Bh) by 122(7A), 122 is added to a file 75 times. It needs two files to hold the answer.

M1

M2
CLRF 2B
CLRF 2C
MOVLW 7Ah
MOVWF 2A,1 MOVLW 4B
ADDWF 2B,1 BTFSS 03,0
GOTO M2
INCF 2C,1
DECFSZ 2A,1
GOTO M1
RETURN ;Clear the receiving file
;Clear the receiving file
;122
;file 1A holds 122
;75
;ADD 75 to file 2B
;Test Carry bit in status
;file. CLEAR = no carry
; SET = carry

The result is a 16 bit binary number of the form: file 2C, file 2B = 0000 0000 0000 0000
To multiply two numbers and obtain a decimal result requires a different program.

Nested Delay
See Delay

Nibble
Nibble is 4 bits - each byte has two nibbles - called the Low-Nibble and High-Nibble. Here is a simple routine that takes the lower nibble and puts it in another file called LowNibble and the high nibble into a file called HighNibble:

movf Byte,w
andlw 0x0F
movwf LowNibble
swapf Byte,w
andlw 0x0F
movwf HighNibble ;move the byte into w
;anding w with 0Fh will make the top 4 bits = 0
;move w to a new file called LowNibble. 1st part finished.
;swap the high nibble with the lower nibble and put in w
;anding w with 0Fh will make the top 4 bits = 0
;move w to a new file called HighNibble. 2nd part finished.
;The lower 4 bits will be in the 4 lower places of LowNibble ;and the 4 upper bits of Byte will be in the 4 lower places of
;HighNibble

OPTION - Option Register
Writing to OPTION Register:

movlw b'00000000'
option

Origin - ORG
This is a pseudo instruction (also called a directive) that tells the assembler where to place the next instruction. ORG must have a value. For ORG 000, the real instruction will be placed at memory location 000.
For ORG 2Ch, the first instruction in Main will be placed at address location 2Ch as shown below:

SetUp

Main

ORG 000
MOVLW 08
MOVWF TRISIO
OPTION 0DFh
- - - - - - - - - -
- - - - - - - - - -
ORG 2Ch
CALL Switch
CALL Display
CALL Beep
GOTO Main ;Start of program in memory
;

;

;Next following instruction will be placed at location 2Ch

Oscillator Calibration value

call        0x3ff
movwf    OSCCAL

org       0x3ff
retlw   0x20

END ;get the calibration value
;calibrate oscillator

;OSCCAL calibration value is located at the last line of
;    program memory and has the instruction to return with
;   20h in W

Output a Table Value see also Table

Table

ADDWF 02h,1
RETLW 3Fh
RETLW 06h
RETLW 5Bh
RETLW 4Fh
RETLW 66h
RETLW 6Dh
RETLW 7Dh
RETLW 07h
RETLW 7Fh
RETLW 6Fh

;Add W to the Program Counter to create a jump.

Output a Value
The output port for a PIC12F629 is actually a FILE or REGISTER! It is file 05.
The 6 lines of the port are called: GP0, GP1, GP2, GP3, GP4 and GP5.
Each line can deliver approx 25mA. The maximum total current for the chip is about 150mA.
An output line can be HIGH or LOW. Each output line corresponds to a bit in the file associated with the port. When the bit is SET, the line is HIGH. When the bit is CLEAR, the line is LOW.
Before you can make a line HIGH or LOW, the file must be "configured." This means each bit must be made an OUTPUT. This is done via the TRISIO file. This file is located at 85h - in Band 1.
Any line can be made either an input or an output at any time during the running of a program and to make a line INPUT, the corresponding bit in the TRISIO file is made "1." To make a line OUTPUT, the corresponding bit in the TRISIO file is made"0."
There are two ways to get to the TRISIO file. One is directly via the instruction:

MOVLW 2Bh
TRISIO ;Load xx10 1011 into W
;Make GP2 and GP4 output.

The other is via the two instructions: BSF 03,5 and BCF 03,5. These instructions allow you to go to bank1 where the TRISIO file is located. It is in Bank1 and the TRISIO file is called 05.

BSF 03,5
MOVLW 3Fh
MOVWF 05
BCF 03,5 ;Go to Bank 1
;Load W with 0011 1111
;Make all GPIO input
;Go to Bank 0 - the program memory area.

Any lines that are made output can be made HIGH or LOW.

MOVLW 16h
MOVWF GPIO ;Load 0001 0110 into W
;Make GP1 and GP2 and GP4 HIGH.

Output 8 bits of a file via bit0 of GPIO:.

Loop movlw    8
movwf    count
btfss      temp,0
bcf         GPIO,0
btfsc      temp,0
bsf         GPIO,0
rrf          temp,f
call        delay
decfsz   count,f
goto      Loop ;
; create file to hold the 8 loops
;
;temp will be 0 so clear bit0 of gpio and send
;temp will be set, so set bit0 of gpio and send
;
;shift temp file so bit1 becomes bit0
;
;
;perform 8 loops

Output Pin Input/Output Pin
Theses are the same terms for a microcontroller pin that accesses the outside world. Each pin is capable of delivering a current of 20mA when HIGH (set) or sinking 20mA when LOW (clear).
You must not prevent the pin going to its full 4.8v HIGH or 0.2v LOW as the MOSFET transistor connected to the pin is microscopically small.
The PIC12F629 has 6 pins with 5 pins configurable as input/output and pin4 configurable as INPUT ONLY.
Pin 7 is General Purpose In/Out (gpio,0)
Pin 6 is General Purpose In/Out (gpio,1)
Pin 5 is General Purpose In/Out (gpio,2)
Pin 4 is input ONLY (gpio,3)
Pin 3 is General Purpose In/Out (gpio,4)
Pin 2 is General Purpose In/Out (gpio,5)
File 6 in the file register holds the data for the 6 pins.
The 6 lower bits of the file hold the data.
When a bit is 0, the output is LOW when a bit is 1, the output is HIGH.
Another register in the file holds the information that determines if the pin is an input or output.
This register is called the trisio register. When a bit is 0, the pin will be an output. When a bit is 1, the pin will be input.
Bit3 of the trisio register can only be 1.
Any pin can be changed from input to output at any time during the running a of a program.
The pins are initially set by the following lines of code, or a combination of "0" and "1:"

bsf              status,rp0      ;bank1
movlw         b'00000000'     ;this will make all pins output (gpio,3 will be input ONLY)
movwf         trisio
bcf              status,rp0      ;bank0

or

bsf              status,rp0      ;bank1
movlw         b'11111111'     ;this will make all pins input
movwf         trisio
bcf              status,rp0      ;bank0

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