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4 LD (HL),C 3 DEFM " ADD HL,HL 3 LD (HL),L 3 LD (DE),A 3 ADD HL,HL 2 the number 2 DEFM " RET 2 SBC HL,DE 2 SBC HL,BC 2 LD HL,STORE 2 LD A,(DE) 2 LD (22529),A 2 LD (22528),A 1 transfer (HL) to (DE), increment HL and DE, decrement BC, set PV flag if BC=0 1 transfer (HL) to (DE), decrement HL, DE, and BC, set PV flag if BC=0 1 the port whose number is in C 1 the memory location (IY) 1 the memory location (IX) 1 the memory location (DE) 1 the memory location (BC) 1 the location (HL) 1 the contents of the Accumulator is eXclusively ORed with 1 the contents of 1 the computer is HALTed until an interrupt comes to awake it again 1 the carry flag is set, ie Set Carry Flag 1 the carry flag is inverted, ie Compliment Carry Flag 1 the alternative AF registers 1 the accumulator is ComPared with 1 the Stack Pointer 1 the Refresh register 1 the RETurn address is POPped from the stack 1 the L register 1 the Interrupt vector register 1 the IY register 1 the IX register 1 the HL register 1 the H register 1 the Flag register 1 the E register 1 the DE register 1 the D register 1 the C register 1 the BC, DE, HL registers are all EXchanged with the alternative set 1 the BC register 1 the B register 1 the Accumulator is logically ORed with 1 the Accumulator is logically ANDed with 1 the Accumulator is NEGated, ie made negative 1 the Accumulator 1 the AF registers 1 search from (HL) Incrementing BC bytes for data in Accumulator 1 search from (HL) Decrementing BC bytes for data in Accumulator 1 rotate the accumulator and carry Right 1 rotate the Accumulator and carry Left 1 rotate the Accumulator Right, shifting bit 0 into Carry 1 rotate the Accumulator Left shifting bit 7 into Carry 1 rotate Right Decimal contents of (HL) with least significant end of Accumulator 1 rotate Left Decimal contents of (HL) with least significant end of Accumulator 1 reSTart at address 1 r single register 1 push the return address to stack and CALL 1 port with the above number 1 perform relative jump to 1 perform jump to 1 output from (HL) to port (C) increment HL, decrement B 1 ouTput to port (C), from block from (HL) Decrementing HL for B bytes 1 ouTput from (HL) to port (C) block from (HL) Incrementing for B bytes 1 oUTput from (HL) to port (C) Decrement HL, decrement B 1 memory location 1 location (IY+offset) 1 location (IX+offset) 1 is loaded with 1 is Shifted Right Logically, 0 is shifted into bit 7 1 is Shifted Right Arithmetically, sign bit unchanged 1 is Shifted Left Arithmetically, 0 is shifted into bit 0 1 is Rotated Right, shifting bit 0 into Carry 1 is Rotated Left shifting bit 7 into Carry 1 is PUSHed onto the stack and the SP decremented by 2 1 is POPped from the stack and the SP incremented by 2 1 is INCremented by 1 1 is EXchanged with 1 is DECremented by 1 1 invert all bits in A register, ie ComPLiment 1 instruction 1 input data from 1 if the Zero flag is set, 1 if the Zero flag is not set, 1 if the Sign flag is set, ie Minus, 1 if the Sign flag is not set, ie Positive, 1 if the Parity flag is sEt, ie Parity is Even, 1 if the Parity flag is nOt set, ie Parity is Odd, 1 if the Carry flag is set, 1 if the Carry flag is not set, 1 iNput into (HL) from port (C) increment HL, decrement B 1 iNput into (HL) from port (C) Decrement HL, decrement B 1 iNput from port (C), into block from (HL) Incrementing HL for B bytes 1 iNput from port (C), into block from (HL) Decrementing HL for B bytes 1 has taken from it the carry and 1 has added to it the carry and 1 has added to it 1 enable Interrupts. NOT PERFORMED BY SIMULATOR. 1 disable Interrupts. NOT PERFORMED BY SIMULATOR. 1 decrement B, if zero continue, if Not Zero perform relative jump to 1 decimal Adjust Accumulator 1 compare (HL) with A, increment HL, decrement BC 1 compare (HL) with A, decrement HL, and BC 1 change Interrupt Mode to 1 block transfer (BC) bytes starting at (HL) to (DE) incrementing 1 block transfer (BC) bytes starting at (HL) to (DE) decrementing 1 and Carry are rotated Left 1 and Carry are Rotated Right 1 There are no double register SUBinstructions. 1 The Accumulator has subtracted from it 1 Space missing 1 SUB (HL) ) 1 SBC HL,BC ) SuBtract from HL with carrySBC HL,DE ) 1 SBC A,r ) SuBtract from A with carrySBC A,(HL)) 1 SBC A,n ) 1 S7:DEFM " EXAMPLE OF REGISTER PAIR ADDITION 1 S6:DEFM " EXAMPLES OF SINGLE REGISTER ADDITION 1 RETurn from Non-maskable interrupt: NOT PERFORMED BY SIMULATOR 1 RETurn from Interrupt: NOT PERFORMED BY SIMULATOR 1 P8:DEFM " We can therefore load a register pair" 1 Offset too big 1 Offset missing 1 Number too large 1 Number missing 1 No OPeration is performed, inspite of this it takes . 1 No DEFB, or DEFW 1 NOT DEFINED 1 Missing space or , 1 Label too long 1 Label not found 1 LD r,(HL) where r is any single register 1 LD dd,nn where dd is any register pair 1 LD dd,(nn) 1 LD A,(nn) where nn is a number 0 - 65535 1 LD (nn),dd 1 Instruction unknown 1 FLAGS$ Registers and Contents % STAC 1 Error after inst. 1 EX5B:DEFM " LD HL,(STORE) 1 EX5A:DEFM " LD DE,8740 1 DEFM "with the contents of a pair of memory" 1 DEFM "using addition to successively multiply by" 1 DEFM "together numbers of any length. 1 DEFM "to the non-valid instructions LD E,(nn)" 1 DEFM "the Lower address. 1 DEFM "the form LD r,r' are usually used to" 1 DEFM "the Low byte is held in the location with" 1 DEFM "results can be displayed easily. This" 1 DEFM "register addition only. The double length" 1 DEFM "register pairs with the contents of" 1 DEFM "register pair into a pair of memory" 1 DEFM "register pair addition, as well, to add" 1 DEFM "numbers are held in BC and DE so that the" 1 DEFM "numbers 8740 and 1260 using single" 1 DEFM "number held in the HL register pair by 10" 1 DEFM "method of addition can be performed using" 1 DEFM "locations, i.e. LD (nn),BC which is" 1 DEFM "locations, with instructions like" 1 DEFM "instructions LD (nn),C and LD (nn+1),B." 1 DEFM "equivalent to the two non-valid" 1 DEFM "displayed to the left of the registers. 1 DEFM "another register pair. Two instructions in" 1 DEFM "and LD D,(nn+1). 1 DEFM "LD DE,(nn). This instruction is equivalent" 1 DEFM " This example effectively multiplies a" 1 DEFM " There are no instructions to load" 1 DEFM " The state of the individual flags are" 1 DEFM " The example adds together the two" 1 DEFM " Similarly, we can load the contents of a" 1 DEFM " STORE DEFB 25 1 DEFM " LOW DEFB 20 1 DEFM " HIGH DEFB 125 1 DEFM " LD HL,STORE 1 DEFM " LD DE,(STORE) 1 DEFM " LD C,A 1 DEFM " LD BC,32021 1 DEFM " LD BC,1260 1 DEFM " LD B,A 1 DEFM " LD A,E 1 DEFM " LD A,D 1 DEFM " LD A,15 1 DEFM " LD (STORE),HL 1 DEFM " LD (HL),0 1 DEFM " LD (DE),A 1 DEFM " LD (BC),A 1 DEFM " ADD HL,DE 1 DEFM " ADD A,C 1 DEFM " ADD A,(HL) 1 DEFM " ADC A,B 1 Cursor keys, delete, and auto-repeat are as standard. BREAK returns you to menu. 1 Can only ADD IX/IY 1 CP (HL) Compares A with memory location 1 Bracket missing 1 All configurations of ADC instructionscan be used with SBC or SuBtract withCarry instructions. The operation issimilar to SUB, except that the result isdecremented by one if the carry flag isset. 1 ADDRESS MACHINE CODE 1 ADD A,r where r is any single 1 ADD A,n where n is a number 0 - 255 1 ADD A,(HL) 1 ADC A,(HL) 1 01 seconds to do it 1 /^3^7^D^Q^^^e^o^v^ 1 . Conventionally" 1 where r and r' are any of the 1 where n is a number 0 - 255 1 nn is a number 0 - 65535 1 n/v instruction not valid 1 following: A,B,C,D,E,H and L. 1 exchanges register contents 1 dd double register* flag affected 1 You are trying to run code in allocated storage area. RET missing? Please EDIT 1 You are about to write to memory which will affect your program. Please edit it. 1 You are about to affect memory area not allocated to you. Please edit program. 1 You may go through the example as manytimes as you like, until you understandit. If you still find difficulty, pressBREAK, skip over the lessons and re-ENTERthe lesson with which you are havingdifficulty. The manual however gives anoutline of each lesson. 1 While running this example try to predictthe state of the Zero flag after theinstruction has been performed. 1 When you do understand the examples giventry modifying them using the editor.Then try entering your own programs. Allprograms should end with RET ( or return).Don't worry if you forget, the simulatorwill tell you. 1 We can also load a memory location withthe contents of the Accumulator withLD (nn),A where nn is the number oraddress of the memory location. 1 We can therefore load a register pairwith the contents of a pair of memorylocations, with instructions likeLD DE,(nn). This instruction is equivalentto the non-valid instructions LD E,(nn)and LD D,(nn+1). 1 We can load any of the register pairswith a number between 0 - 65535 directlyusing instructions like LD HL,nn. 1 We can also load any of the registerswith a number, n, between 0 and 255directly, with instructions like LD C,123.We shall discuss later from where thenumber is copied. Suffice to say, at thisstage, that instructions are stored asnumbers. For example LD A,B is stored as78. Look up in Appendix A of your SpectrumManual LD A,B and the number 78. Someinstructions like LD A,B are stored as onenumber, others take up to four. 1 Use of the BC and DE registers forindirect addressing is limited to the Aregister. i.e. LD (DE),A ; LD A,(BC) etc. 1 Up to now we have only used instructionsin which memory locations have beenspecified directly in the instruction.Another useful method of specifying amemory location is to use a number held ina register pair, known as indirectaddressing. The instruction LD B,(HL) forexample allows us to load or copy to the Bregister the contents of the memorylocation whose address is in the HLregister pair. 1 Try to predict the state of the Zero andCarry flags before performing thecomparison. In the next lessons we will beusing these flags extensively, to producemore interesting examples. 1 This example subtracts 1260 from 8740using only single register subtraction.The two numbers are held in allocatedmemory locations this time. 1 This example effectively multiplies anumber held in the HL register pair by 10using addition to successively multiply by2. 1 This method of subtraction can beextended to any length number and registerpair subtraction. 1 These instructions are primarily usedwhere counters are required. The operationon register pairs is also useful insequential operations on memory locationsutilising indirect addressing. 1 These examples illustrate indirectaddressing. At this stage it is impossibleto demonstrate its usefulness. It isemployed extensive in later examples 1 There are too many registers called up, to display. Program will RUN as normal. 1 There is one instruction similar tothis type: EX DE,HL. It EXchanges thecontents of the DE register pair with thecontents of the HL register pair. 1 The two registers hold different parts ofa number. Consider the decimal number 27.We can think of this as having two parts;the high part ( or byte) is the 2 since itrepresents 2*10, the low part (or byte) isthe 7, since it only represents 7*1. Thetotal number is 2*10+7*1=27. Each digitcan only be 0 - 9 i.e. 10 differentnumbers. 1 The step by step instructions making up aprogram are stored in memory, a series ofsimilar registers or memory locations,external to the Z80 chip. 65536 memorylocations can be accessed. They aredesignated by their number between 0 and65535. It takes the Z80 longer to accessmemory than its own internal registers. 1 The stack pointer is outside allocated memory area. Please edit program. 1 The simulator will display the contentsof this memory location, in decimal, inthe second column. 1 The program has been completed. You may EDIT or reRUN. Exit by pressing BREAK. 1 The last arithmetic instructions to bediscussed can be performed on any singleor double register(s). These are INC andDEC. INC increments (or increases) thecontents of the register, or memorylocation indirectly addressed by the HLregister pair, by one. DEC decrements (ordecreases ) the contents of the register,or memory location indirectly addressed bythe HL register pair, by one. 1 The fact that a single register can onlyhold numbers up to 255 and the totalmemory available is up to 65535, is alimitation. For this reason there are awhole set of instructions on the Z80 thatdeal with registers in pairs. The pairsare BC, DE, and HL register pairs. 1 The assembler, that converts instructionsinto machine code, will accept Labels.Instead of putting an address into theprogram, we can give it a name. Theassembler will then allocate a memorylocation to it. The name must be called upin the program with its initial conditionusing the instruction DEFB, DEFine Byte. 1 The zero flag, like the carry flag, isunaffected by any LD or EX instructions. 1 The two types of instructions discussed( LD r,r' and LD r,n ) can involve any ofthe registers considered. Only the Aregister can be loaded with the contentsof a memory location. The instruction ofthe general form LD A,(nn) loads or copiesthe contents of memory location nn( a number between 0 and 65535 ) into theA register. 1 The state of the individual flags aredisplayed to the left of the registers. 1 The examples that follow use the colouras well as labels, so expect some colourchanges. 1 The example illustrates each type ofinstruction that loads register pairs. Italso demonstrates that a register/memorypair are still two individual registers ormemory locations and can be treated assuch. 1 The carry flag is not affected by eitherof these instructions. 1 The carry flag can be set to a "1" withthe instruction SCF or Set Carry Flag.Although there are no specificinstructions to clear the carry flag to"0" there is an instruction to invert itCCF or Compliment Carry Flag. We shall seelater that all logic instructions do clearthe carry flag. 1 The address in the first column is thelow byte address. The second columndisplays the contents of the pair ofmemory locations as a single number. 1 The Z80 is the microprocessor at theheart of your Spectrum. This program willteach you the use of all the instructionsavailable on the Z80, in a series ofsimple progressive lessons. 1 The example adds together the twonumbers 8740 and 1260 using singleregister addition only. The double lengthnumbers are held in BC and DE so that theresults can be displayed easily. Thismethod of addition can be performed usingregister pair addition, as well, to addtogether numbers of any length. 1 The load instruction is normallyabbreviated to LD. The simplest form ofload copies data from one register toanother, i.e. LD A,B . 1 THE ZERO FLAG 1 Summary - zero and carry flags 1 Summary - increment and decrement 1 Summary - comparisons 1 So far all instructions we have discussedthat affect the Carry or Zero flags alsoaffect the register concerned. There are anumber of useful instructions that onlyaffect flags. The compare or CPinstruction is one of these. 1 Single and double register additions willobviously only give the correct result ifthe answer is less than the maximum numberthe register(s) can hold. If it is greaterthan this a carry is generated. Theprocessor holds this single bit ofinformation or flag, so that action can betaken over the occurrence of the carry. Ifthere has been a carry on the lastarithmetic operation the carry is said tobe set to a "1". If not set it is said tobe a "0". 1 Single register subtraction takes placewith the Accumulator. All the forms of ADDcan be used in subtract. The abbreviationor mnemonic SUB is always written withoutthe A, which is implied. Hence theinstructions are SUB n, SUB r, andSUB (HL). Again the result is held in theAccumulator. The carry flag is set to a"1" if the result is outside the range 0-255. 1 Since double register subtraction canonly be performed with carry, the state ofthe carry flag prior to SBC HL,BC, andSBC HL,DE is important, and should be "0". 1 Similarly, memory locations can be loadedindirectly from any single register usingthe contents of the HL register pair asaddress i.e. LD (HL),C. 1 Similarly, we can load the contents of aregister pair into a pair of memorylocations, i.e. LD (nn),BC which isequivalent to the two non-validinstructions LD (nn),C and LD (nn+1),B. There are no instructions to loadregister pairs with the contents ofanother register pair. Two instructions inthe form LD r,r' are usually used toperform such an operation. 1 Set Carry Flag 1 SUMMARY - subtract with carry 1 SUBTRACTION AND THE CARRY FLAG 1 STORE DEFW 6000 1 STORE DEFW 32000 1 STORE DEFB 7 1 STORE DEFB 6 1 STORE DEFB 25 1 SOURCE CODE 1 SIMPLE LOAD INSTRUCTIONS 1 Return to operating system 1 Remember, it is impossible for a programto destroy your computer. You'll need aa hammer to do that! 1 Registers are like pigeon holes in whichnumbers can be stored. A single registercan store any number between 0 and 255.The Z80 has many such registers. Initiallywe shall consider only the more generalones: designated A,B,C,D,E,H and L. The A( commonly called the Accumulator ) is themost important, since more instructionsinvolve this register than any other. 1 Register pair addition is performed inconjunction with the HL register pair, andcan only involve BC or DE ( i.e. ADD HL,BCor ADD HL,DE ). Again the result is heldin the HL register pair, and the otherregister pair is unaffected. 1 REGISTERS and MEMORY 1 REGISTER PAIRS 1 REGISTER PAIR EXAMPLES 1 Program stopped. You may re-RUN, EDIT or press BREAK to return to menu. 1 Program has successfully assembled. Press RUN, EDIT, or exit by pressing BREAK. 1 Program counter has jumped to non-valid address. EDIT or reRUN program. 1 Proceed through the menu by pressingENTER to begin the highlighted lesson orexample, and SPACE to jump to the next. Atanytime BREAK will return you to themenu. 1 Press SPACE to select and ENTER to start 1 Press SPACE to continue. 1 Press RUN to begin example, EDIT to edit, and BREAK to return to menu. 1 Please confirm disk loading required Y/N 1 Perhaps a better description of load thanthe conventional one is copy, since a loadinstruction copies the number held in aregister or memory location into anotherregister or memory location. As with allcopying the original remains unchanged. 1 NUM2 DEFW 8740 1 NUM1 DEFW 1260 1 Loading lessons 26-35 1 Loading lessons 18-25 1 Loading lessons 10-17 1 Loading lessons 1-9 1 Loading has been stopped 1 Loading error 1 Load further lessons from disk 1 Like ADC instructions SBC instructionscan be strung together to subtract anylength number. 1 Lessons 1 - 9 1 LOW DEFB 20 1 LOW DEFB 0 1 LD HL,NUM1 1 LD HL,LOW 1 LD HL,257 1 LD HL,23040 1 LD HL,(STORE) 1 LD DE,8740 1 LD DE,256 1 LD A,(STORE) 1 Just as we can combine two registers tohold numbers up to 65535, we can combineadjacent memory locations. Conventionallythe Low byte is held in the location withthe Lower address. 1 It is only affected by double registerarithmetic operations involving the carryflag, i.e. only affected by ADC HL,dd orSBC HL,dd. 1 In these abbreviationed instructions( mnemonics ), it is conventional to putthe register affected first, followed bythe register from which the information iscopied. Hence LD A,B copies the contentsof B into A or Accumulator. 1 If n is the number with which A iscompared, then the following results :- 1 INTRODUCTION TO RUNNING SIMULATOR 1 INTRODUCTION 1 INDIRECT ADDRESSING 1 INC and DEC really only become useful inconjunction with instructions to beintroduced shortly. 1 HIGH DEFB 125 1 HIGH DEFB 0 1 Ex - zero flag 1 Ex - single register addition 1 Ex - simple load instructions 1 Ex - register subtraction 1 Ex - register pair subtraction 1 Ex - register pair loading 1 Ex - register pair addition 1 Ex - indirect addressing 1 Ex - inc and dec instructions 1 Ex - comparison instructions 1 EXAMPLES OF ZERO FLAG 1 EXAMPLES OF INDIRECT ADDRESSING 1 EXAMPLES OF COMPARE 1 EXAMPLE OF REGISTER PAIR ADDITION 1 EXAMPLE OF INCREMENT AND DECREMENT 1 Disk V1.0 (c) HanSoft '85 1 DEFM " LD DE,22528 1 DEFB is an assembler instruction not aZ80 instruction. The allocated memoryaddress is given in the first column. 1 Compliment Carry Flag 1 Compares A with register r 1 Compares A with n ( 0 - 255) 1 Colour is used to illustrate registerpair subtraction. Although ADC and SBC mayrequire the Carry flag to be cleared firstif the previous calculation NEVER resultsin a carry being generated, this step maybe omitted. However it is often better tobe safe and include it, than look for therandomly occurring fault that it cangenerate. 1 CP compares the contents of the Aregister with a number (CP n), anotherregister (CP r), or any memory locationindirectly addressed through the HLregister pair ( CP (HL) ). The compareinstruction is effectively SUB but theresult does not affect the contents of theA register. 1 Both single register and register pairaddition are possible on the Z80. 1 Before each instruction is executed theinstruction is described in ENGLISH. Tryto work out what should happen beforepressing any key to perform theinstruction. 1 BC, DE, and HL. 1 At present the programs that can bewritten are somewhat limited. 1 Another very useful flag included in allprocessors is the Zero flag. This flag isset to "1" if the result of any singleregister arithmetic operation is zero.Otherwise it is cleared to"0". 1 Another assembler instruction isintroduced, the DEFW instruction. Theassembler allocates 2 memory locations tothe associated label. The number after theDEFW sets the initial conditions. 1 An area of memory that illustrates wellthe use of instructions is the screen.This area has the following addresses:- 1 All single registers can be loaded usingthe HL register pair as a pointer. 1 All examples are run using the Simulator.At this stage the only areas of thesimulator screen to consider are theSource Code ( the third column that holdsthe instructions ) and the area at thebottom of the screen, which displays thecontents of the registers. Other areaswill be described as they are required. 1 All other single registers cannot beloaded directly from a memory location.Such operations require two instructionsvia the A register. 1 All single register additions areperformed with the Accumulator. A number(i.e. ADD A,6), the contents of a register(i.e. ADD A,B), or the contents of anindirectly addressed memory location usingthe HL register pair (i.e. ADD A,(HL) )can be added to the Accumulator. Theresult is held in the Accumulator. Thesource of the addition is unaffected. 1 ADDITIONS AND THE CARRY FLAG 1 ADC instructions can be strung togetherto perform the addition of two numbers ofany length, as the examples will show. 1 A,B,C,D,E,H, or L. 1 A second form of addition is available onthe Z80, for both single and multipleregisters, known as add with carry;abbreviated to ADC. They are similar toADD except that if the Carry flag is setbefore the addition the result isincremented by one. All previouslymentioned ADD instructions can beperformed as ADC. 1 A single register can hold 0-255, 256different numbers. If we put two registersside by side, such as HL, the H registerholding the High byte and the L holdingthe Low byte, then we can hold in theregister pair the number H*256+L*1 in thesame way as 27=2*10+7*1. The maximum thatcan be held in a register pair istherefore 255 * 256 + 255 = 65535. Byconvention the high byte is stored inthe first register in the register pairname. 1 9. Compare 1 8. Zero Flag 1 7. Increment and Decrement 1 6. Subtraction and the Carry Flag 1 5. Addition and the Carry Flag 1 4. Indirect Addressing 1 3. Register Pairs 1 22528 to 23295 1 2. Simple Load Instructions 1 16384 to 22527 1 1. Registers and Memory 1 . flag not affected 1 ) SUBtract from A, n, r, or 1 & clears all ENTER tabs to next line STOP assembles SPACE tabs in label are 1 SUB (HL) 1 SBC A,(HL) 1 Loading error 1 LD HL,HIGH 1 LD HL,22550 1 LD HL,22528 1 LD HL,1000 1 LD HL,(LOW) 1 LD DE,NUM2 1 LD DE,256 1 LD DE,22528 1 LD DE,(STORE) 1 LD C,(HL) 1 LD BC,32021 1 LD BC,32 1 LD BC,1260 1 LD B,(HL) 1 LD A,255 1 LD A,(BC) 1 LD A,(22530) 1 LD (STORE),HL 1 LD (STORE),DE 1 LD (STORE),A 1 LD (LOW),DE 1 LD (HL),0 1 LD (HIGH),A 1 LD (BC),A 1 Error found during assembly. Please correct before running program. 1 EXAMPLE USING REGISTER PAIR SUBTRACTION 1 EX DE,HL 1 DEC (HL) 1 After each lesson, step by step examplesare given. To further improve yourunderstanding of the topic, you may thenmodify or rewrite the examples, and runthem without fear of crashing the system. 1 ADD HL,DE 1 ADD A,230 1 ADD A,(HL) 1 ADC HL,HL 1 Summary - loading register pairs 1 INCREMENT AND DECREMENT INSTRUCTIONS 1 EXAMPLE OF SINGLE REGISTER SUBTRACTION 1 Detail area 1 Colour area 1 ASSEMBLED CODE LABELS INSTRUCTIONS 1 Summary - Loading single registers 1 Summary - indirect addressing 1 Summary - addition 1 Enter the Z-80 simulator ? Y/N 1 EXAMPLES OF SINGLE REGISTER ADDITION