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How do you set a port to be input or output?
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mov !rportname, #constantA 1 in binary represents an input; 0 an outputex: mov !rb, #%11111111; set all of port b to input
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How do you access a port's directional register?
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!rportnameex: !rbNote: each bit in the 8-bit port register represents the respective i/o pin on that port
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What must you do to keep the watchdog from resetting the SX unexpectedly?
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Clear the watchdog periodically within it's time valueex: clr !wdt; clears watchdog timer
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ds
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reserve bytes for a variableex: var1 ds 2var1 is now two bytes long(put an org statement beforehand to use specific registers)
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What's wrong with this?var1 ds 2mov w,var2
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Only the first byte of var1 is stored into w; use var1+1 to access the second byte of var1 (note: w is a one byte accumulator)
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setb
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Set Bitsets one bit in a registerex: setb
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What is compatability mode?
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A directive in the device preprocessor statement; slows everything down so that the SX can run code written for other microcontrollers
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MODE register
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a
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FSR (File Select Register)
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a
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equ=
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equateex: var1 equ 8var1 points to register 8ex: var1 equ $8var1 holds the hex value $8
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clr
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clearclears a byte, or a bit of a byteex: clr rb; sets rb to 0
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add pc,w
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skip w steps
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clc
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clear carry bit of status register
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and
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and's var2 with var1 (or w), and stores it into var1 (or w). var2 can be replaced by a constantuasge: and w,var2
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jnz
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jump if zero flag is 0 (cleared)ex: jnz testwill jump to label test only if the z flag is 0
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jmp $+3
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jump 3 instructions ahead
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jb
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jump if bit is setex: jb rb.0,testwill jump to label test when bit 0 of rb is 1
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IREAD
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a
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What's the difference between equ and = ?
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when equ is used, the value of var1 cannot be changedwhen = is used, the value of var1 can be changed
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:
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local label
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registers $00-$07
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special
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mov w,--8
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8-1==w8==8
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register W
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accumulator
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!
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directional register
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STATUS register
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a
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stc
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set carry bit of status register
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var.0
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first bit of var
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How do you multiply a register by 2?
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shift the bits left 1
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or
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or's var2 with var1 (or w), and stores it into var1 (or w). var2 can be replaced by a constantuasge: or w,var2
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What are local labels?
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labels within labelsex: label1 :label2; label2 is only visible within label1
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What happens when you reset the SX while it's running?
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All ports change back to inputs
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stz
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set zero bit of status register
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xor
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xor's var2 with var1 (or w), and stores it into var1 (or w). var2 can be replaced by a constantuasge: xor w,var2
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What are the watchdog prescaler values?
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a
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what's confusing about org?
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Can refer to either data space or program space
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djnz
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decrements a register by 1 and stores the result back into the register, and if it's zero, jumps to the specified label
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jmp
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jumpused to jump to labels or different memory adressesex: jmp start; jumps to label start
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mov with anything other than w
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w gets destroyed
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rl
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rotate bits left (bit 7 shifts to carry flag, carry flag shifts to bit 0)
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jnb
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jump if bit is 0 (cleared)ex: jnb rb.0,testwill jump to label test if bit 0 of rb is 0
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rr
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rotate bits right (bit 0 shifts to carry flag, carry flag shifts to bit 7)
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dec 8
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8-1==8
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jc
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jump if carry flag is setex: jc testwill jump to label test if the carry flag is set; else the program will continue as normal
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add
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Adds two registers together and stores them in the formerex: add w,#3; w=w+3
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How do you change logic levels of a port?
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mov rportname, #constantA 1 in binary represents high; 0 lowex: mov rb, #00000000; set all of port b to logic level 0 (low)
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nop
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No Operation Performed
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registers $08-$1F
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general purpose
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inc
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incrementincrements a register by 1ex: inc w; w+1
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#
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constant
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clz
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clear zero bit of status register
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What is the size of a word instruction?
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12 bits
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mov var1-w
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var1=var1-w
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PC (Program Counter)
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a
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What's wrong with this?mov var2,var1mov var3,var1
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Since there's no instruction to move one variable into another, var1 is moved into w, and then into the destination variable. Here, var1 is loaded into w twice, which is wasteful
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What can't clr be used with?
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clearing a port directional registerex: clr !rb; this won't work!
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test
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tests for equality between two registersex: test var1,var2basically it does var2-var1 and checks if the zero flag is set
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How to you increment/decrement a register without modifying it?
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You use mov w,++register or mov w,--registerex: mov w,++reg; w=reg+1 reg==regmov w,--reg; w=reg-1 reg==reg
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What is the size of a data word?
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8 bits
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jnc
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jump if carry flag is 0ex: jnc test
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How do you divide a register by 2?
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shift the bits right 1
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jz
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jump if zero flag is setex: jz testwill jump to label test if the zero flag is set; else the program will continue as normal
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ijnz
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increments a register by 1 and stores the result back into the register, and if it's zero, jumps to the specified label
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