CP/M/CPM_CDROM.iso/beehive/program/xasm.arc/XASM86.HLP

Text File | 1990-08-26 | 22.0 KB | 592 lines

Introductioε t∩ thσ 808╢ architecture.
Addessinτ modes.
The instruction set.
Assembler Syntax of intructions and directives.
Assembler Directives.
Assembler Operators
Invocation of XASM86.COM
Example listing with comments
:Thσ 808╢ ha≤ ß 2░ bi⌠ addres≤ bus¼ bu⌠ onl∙ 1╢ bi⌠ registers« T∩ ì
accommodatσ this¼á thσ SEGMEN╘ registers¼á (CS,DS,SS,ES⌐ arσ useΣ ì
t∩á suppl∙ thσ mos⌠ significan⌠ 1╢ oµ thσ 2░ bi⌠ physica∞ addres≤ ì
lines«á Thσ lowe≥ 1╢ bit≤ arσ supplieΣ froφ thσ registe≥ useΣá iε ì
thσ operation« Thσ segmen⌠ register≤ iε detai∞ are:

ááááááááá CS-The code segment register.

áááááááá Al∞ executablσ codσ mus⌠ residσ iε thσ codσ segment¼ anΣ ì
áááááááái⌠á use≤ thσ intructioε pointer(IP⌐ t∩ providσ thσ 1╢ bi⌠ ì
ááááááááoffset within the segment.

áááááááá  DS-The data segment register.

ááááááááThσá datßá useΣá b∙á ß prograφá i≤á accessed(b∙á default⌐ ì
ááááááááusinτ thσ D╙ registe≥ witΦ thσ offse⌠ addres≤ withiεá thσ ì
áááááááásegmen⌠á provideΣ b∙ thσ addressinτ mode (seσá addressinτ ì
áááááááámodes)«á Iµá anothe≥ segmen⌠ hold≤ thσ datß t∩ bσ useΣ b∙ ì
ááááááááthσá program¼á thσá segmen⌠ ma∙ bσ specifieΣá withiεá thσ ì
ááááááááinstructioεá b∙á usinτá ß SEGMEN╘á OVER-RID┼á PREFIX.(seσ ì
        later)
áááááááá  SS-The stack segment register.

ááááááááThσá datßá iεá ßá prograφá PUSHE─á anΣá POPPE─á ont∩á thσ ì
áááááááástack(usinτ thσ S╨ a≤ thσ offse⌠ withiε thσ segmen⌠) mus⌠ ì
ááááááááliσ withiε thσ stacδ segment« Othe≥ register≤ ma∙ usσ thσ ì
áááááááástacδ segmen⌠ b∙ usinτ thσ appropriatσ SEGMEN╘á OVER-RID┼ ì
ááááááááPREFIX.

áááááááá  ES-The extra segment register.

ááááááááAl∞á strinτ operation≤ usσ thσ extrß segmen⌠ registe≥á a≤ ì
   áááááthe destination segment.
REGISTERS

Thσá 808╢ ha≤ ┤ 1╢ bi⌠ register≤ tha⌠ caε bσ useΣ a≤ accumulator≤ ì
fo≥ mos⌠ purposes«á The∙ arσ AX,BX,C╪ AN─ DX« Thesσ register≤ caε ì
bσ operateΣ oε a≤ 1╢ bi⌠ registers¼á a≤ specifieΣ above,(e.g« AX⌐ ì
o≥ a≤ independen⌠ ╕ bi⌠ registers¼ b∙ specifyinτ thσ registe≥ anΣ ì
thσ uppe≥ o≥ lowe≥ ╕ bits«á Fo≥ example¼á thσ 1╢ bi⌠ registe≥á A╪ ì
caεá bσ specifieΣ a≤ thσ concatenatioε oµ thσ lowe≥ ╕á bits¼á thσ ì
registe≥ A╠ anΣ thσ uppe≥ ╕ bits¼ thσ registe≥ AH« Apar⌠ froφ thσ ì
genera∞á arthimetiπ functions¼á eacΦ oµ thesσ ┤á  register≤á havσ ì
somσ implieΣ specia∞ function.
ááááááááA╪á    Thi≤á registe≥á mus⌠ bσ useΣ fo≥ al∞á I╬á anΣá OU╘ ì
ááááááááinstructions¼á anΣá fo≥ al∞ multiplicatioεá anΣá divisioε ì
ááááááááinstructions«á Also¼á specifyinτá thi≤á registe≥á a≤á thσ ì
áááááááásourcσá o≥á destinatioεá fo≥á direc⌠á offse⌠á storinτá o≥ ì
ááááááááretrieving of data, uses one less instruction byte.

ááááááááB╪á    Thi≤ registe≥ caε bσ useΣ a≤ aε inde° registe≥á t∩ ì
áááááááápoin⌠á int∩á thσá datßá segment¼á togethe≥á witΦá anothe≥ ì
ááááááááregister or offset.(see addressing modes)

ááááááááC╪á    Thi≤á i≤á ß genera∞ coun⌠ registe≥á fo≥á usσá witΦ ì
ááááááááinstruction≤á sucΦá a≤á decremen⌠á C╪á anΣá jum≡á iµá no⌠ ì
áááááááázero(LOOP⌐á o≥á fo≥ variablσ shif⌠ instruction≤á sucΦá a≤ ì
ááááááááshif⌠ registe≥ ε times¼ wherσ ε i≤ helΣ iε CL¿ SH╠ AX,CL)

ááááááááD╪    Thi≤ registe≥ i≤ useΣ fo≥ variablσ por⌠ addressing¼ ì
ááááááááwherσá thσ por⌠ addres≤ i≤ froφ ░ t∩ FFF╞ h«á I⌠ i≤á als∩ ì
ááááááááuseΣ a≤ aε extensioε registe≥ t∩ A╪ fo≥ 3▓ bi⌠ operation≤ ì
   áááááinvolved with multiplication and division.
ááááááááB╨á anΣ S╨ Thesσ arσ 1╢ bi⌠ pointe≥á registers¼á anΣá arσ ì
ááááááááuseΣ t∩ poin⌠ int∩ thσ stacδ segment« Al∞ PUSHe≤ anΣ POP≤ ì
ááááááááusσá S╨á anΣ B╨ i≤ useΣ t∩ acces≤ datß oε thσá stacδá no⌠ ì
áááááááápointeΣ t∩ b∙ SP.

ááááááááS╔ anΣ D╔ Thesσ arσ 1╢ bi⌠ inde° registers¼ useΣ t∩ poin⌠ ì
ááááááááint∩ thσ datß anΣ extrß segments.

ááááááááI╨ Thi≤ i≤ thσ instructioε pointer¼á ß 1╢ bi⌠ registe≥ t∩ ì
áááááááápoin⌠á int∩á thσá codσ segmen⌠ thσá thσá nex⌠á executablσ ì
ááááááááinstruction.
ááááááááFLA╟ register«á Thi≤ 1╢ bi⌠ registe≥ hold≤ thσ condition≤ ì
ááááááááof the last applicable operation as follows:-

áááááááá      bit 15 [x x x x.OF DF IF TF.SF ZF x AF.x PF x CF]
ááááááááwhere x is undefined, and the following are:-
áááááááá  OF Set if result caused an overflow (2's complement)
áááááááá  D╞ Se⌠ b∙ softwarσ t∩ causσ aut∩ IN├ o≥ DE├
áááááááá  IF Set by software for interrupt enable
áááááááá  TF TRAP-When set causes interrupt after one instruction
áááááááá  SF Set if instruction caused msb to be set.(sign)
áááááááá  ZF Set if instruction resulted in zero
áááááááá  AF Set if a carry occurred between nibbles
áááááááá  PF Parity flag,set if parity even
   ááááá  CF Set if carry occurred from msb(or borrow)
:Addressinτ modes
Thσá followinτá tablσá give≤ thσ ful∞ se⌠á oµá possiblσá registe≥ ì
to/froφ memor∙ addressinτ modes¼ anΣ thσ defaul⌠ segmen⌠ tha⌠ thσ ì
offse⌠á i≤á placeΣ in«á BX,S╔ anΣ D╔ implicitl∙ addres≤ thσá datß ì
segment¼á whilσá an∙á combinatioε witΦ B╨ wil∞ acces≤á thσá stacδ ì
segment« Over-ridσ prefixe≤ arσ allowed.
áááááááá       offset              default segment register
áááááááá       (BX)                DS
áááááááá       DISP16              DS
áááááááá       (DI)                DS
áááááááá       (SI)                DS
áááááááá       (BP)+(DI)           SS
áááááááá       (BP)+(SI)           SS
áááááááá       (BX)+(DI)           DS
áááááááá       (BX)+(SI)           DS

áááááááá       (BX)+DISP8-16       DS
áááááááá       (BP)+DISP8-16       SS
áááááááá       (DI)+DISP8-16       DS
áááááááá       (SI)+DISP8-16       DS
áááááááá       (BP)+(DI)+DISP8-16  SS
áááááááá       (BP)+(SI)+DISP8-16  SS
áááááááá       (BX)+(DI)+DISP8-16  DS
áááááááá       (BX)+(SI)+DISP8-16  DS
String operations
Variou≤ onσ bytσ instruction≤ perforφ primitivσ strinτ operation≤ ì
fo≥ thσ manipulatioε oµ continuou≤ datß strings« Thesσ operation≤ ì
ma∙á bσá performeΣ repeatedl∙ b∙ precedinτ thσ instructioεá b∙á ß ì
repeat prefix.( see REP).
Al∞á thσ strinτ operation≤ usσ S╔ a≤ thσ source¿ defaul⌠á t∩á thσ ì
datß segment¼á anΣ ma∙ usσ segmen⌠ over-ride)¼á anΣ usσ D╔ a≤ thσ ì
destination(mus⌠áá bσá iεá extrßá segment)«áá Aut∩á incremen⌠á o≥ ì
decrement of the registers is specified by the diection flag(DF).
:Thσáá 808╢áá instructioεá set«áá Iεá al∞á cases,wherσáá meφáá i≤ ì
specified, reg may be used

Data Transfer

MOV         MOVE
PUSH        PUSH ONTO STACK
POP         POP FROM STACK
XCHG        EXCHANGE
IN          IN FROM PORT
OUT         OUT TO PORT
XLAT        TRANSLATE BYTE TO AL
LEA         LOAD EFFECTIVE ADDRESS
LDS         LOAD DOUBLE WORD TO DS (AND ANOTHER REGISTER)
LES         LOAD DOUBLE WORD TO ES (AND ANOTHER)
LAHF        LOAD AH WITH FLAGS
SAHF        STORE AH INTO FLAGS
PUSHF       PUSH FLAGS ONTO STACK
POPF        POP FLAGS FROM STACK
Arithmetic

ADD         ADD
ADC         ADD WITH CARRY
INC         INCREMENT
SUB         SUBTRACT
SBB         SUBRACT WITH BORROW(CARRY FLAG)
DEC         DECREMENT
AAA         ASCII ADJUST FOR ADD
DAA         DECIMAL ADJUST FOR ADD
AAS         ASCII ADJUST FOR SUBRACT
DAS         DECIMAL ADJUST FOR SUBTRACT
NEG         CHANGE SIGN( 2's complement)
CMP         COMPARE
MUL         MULTIPLY (unsigned)
IMUL        MULTIPLY (signed)
AAM         ASCII ADJUST FOR MULTIPLY
DIV         DIVIDE (unsigned)
IDIV        DIVIDE (signed)
AAD         ASCII ADJUST FOR DIVIDE
CBW         CONVERT BYTE TO WORD
CWD         CONVERT WORD TO DOUBLE WORD
Logic

NOT         LOGICAL INVERSION
SHL(SAL)    SHIFT LOGICAL(ARITHMETIC) LEFT
SHR         SHIFT LOGICAL RIGHT
SAR         SHIFT ARITHMETIC RIGHT
ROL         ROTATE LEFT
ROR         ROTATE RIGHT
RCL         ROTATE THRU' CARRY LEFT
RCR         ROTATE THRU' CARRY RIGHT
AND         LOGICAL AND
TEST        AND TO FLAGS, NO RESULT
OR          LOGICAL OR
XOR         EXCLUSIVE OR
Strings

REP
REPNZ
REPZ        REPEAT PREFIX
MOVS        MOVE STRING
CMPS        COMPARE STRINGS
SCAS        SCAN STRING
LODS        LOAD STRING
STOS        STORE STRING
Control transfer

CALL        CALL (direct or indirect,with in a segment)
CALLF       CALL (direct or indirect,to another segment)
JMP         JUMP (disp16,direct or indirect)
JMPF        JUMP (direct or indirect,to another segment)
JMPS        JUMP (direct,disp8,-128,+127 bytes)
RET         RETURN FROM CALL WITHIN SEGMENT(optional adding to SP)
RETF        RETURN FROM CALL FROM ANOTHER SEG(optional add to SP)
JE(JZ)      JMP IF EQUAL(ZERO)
JL(JNGE)    JMP ON LESS THAN
JLE(JNG)    JMP ON LESS THAN OR EQUAL
JB(JNAE)    JMP ON BELOW( NOT ABOVE)
JBE(JNA)    JMP ON BELOW OR EQUAL
JP(JPE)     JMP ON PARITY EVEN
JO          JMP ON OVERFLOW
JS          JMP ON SIGN
JNE(JNZ)    JMP ON NOT EQUAL
JNL(JGE)    JMP ON GREATER THAN OR EQUAL
JNLE(JG)    JMP ON GREATER THAN
JNB(JAE)    JMP ON ABOVE OR EQUAL
JNBE(JA)    JMP ON ABOVE
JNP(JPO)    JMP ON NOT PARITY(PARITY ODD)
JNO         JMP ON NOT OVERFLOW
JNS         JMP ON NOT SIGN
JC          JMP ON CARRY(Same as JB)
JNC         JMP ON NOT CARRY(Same as JNB)
LOOP        LOOP CX TIMES
LOOPZ
LOOPE       LOOP CX TIMES WHILE ZERO(EQUAL)
LOOPNZ
LOOPNE      LOOP CX TIMES WHILE NOT ZERO
JCXZ        JUMP IF CX NOT ZERO( no flags used)

*¬ Abovσ anΣ belo≈ refe≥ t∩ thσ reletionshi≡ betweeε tw∩ unsigneΣ ì
values, while greater and less refer to signed values **
Interrupts

INT         INTERRUPT
INTO        INTERRUPT ON OVERFLOW
IRET        INTERRUPT RETURN

Processor Control

CLC         CLEAR CARRY FLAG
CMC         COMPLEMENT CARRY FLAG
STC         SET CARRY FLAG
NOP         NO OPERATION (ACTUALLY XCHG AX,AX)
CLD         CLEAR DIRECTION FLAG
STD         SET DIRECTION FLAG
CLI         CLEAR INTERRUPT ENABLE FLAG
STI         SET INTERRUPT ENABLE FLAG
HLT         PROCCESSOR HALT
WAIT        WAIT UNTIL TEST PIN IS ASSERTED
LOCK        LOCK BUS FROM OTHER USERS
ESC         ESCAPE TO EXTERNAL DEVICE ON BUS
Use of segment over-ride prefixes

Operand  register     default             with over-ride
IP( code address)     CS                  NEVER
SP( stack address)    SS                  NEVER
BP( stack marker)     SS                  DS or ES or CS
SI or DI( not strings)DS                  SS or ES or CS
SI (source strings)   DS                  SS or ES or CS
DI (dest. strings)    ES                  NEVER
:Assembler syntax of intructions and directives.

The following is the syntax for an instuction statement.

{label:}   {prefix}  Mnemonic   {Operand(s)}   {;comment}

where the fields are as follows

label║á         ┴ásymbo∞á followeΣ b∙ ":ó define≤ ß labe∞ a⌠á thσ                                 ì
               curren⌠á valuσá oµá thσ locatioεá counte≥á iεá thσ                  ì
               curren⌠ segment.(optional)

prefi°á         Certaiεá machinσ instruction≤ sucΦá a≤á LOC╦á anΣ ì
               segmen⌠á over-ride≤ ma∙ prefi° othe≥ instructions« ì
               (optional)

mnemoniπá       ┴ symbo∞ defineΣ a≤ ß machinσá instruction«á Thi≤ ì
               fielΣá i≤á optiona∞ unles≤ precedeΣá b∙á ßá prefi° ì
               instruction.
operand(s)      Instructions may have 0,1,2 operands.

;commen⌠        An∙ ╗ appearinτ outsidσ ß characte≥ strinτ begin≤ ì
               ß comment¼ whicΦ i≤ endeΣ by<CR>.(optional)

The following is the syntax for a directive statement.

{name}     directive       operand(s)        {;comment}

 where the fields are defined as follows.

name           Unlike the label field of an instruction,the name
               field is NEVER terminated with a colon. Directive
               names are legal only for DB,DW,DD,RS and EQU.

directive      A keyword described under Assembler Directives.

operands       Analogous to operands for instruction mnemonics.

;comment       Exactly as instructions
:Assembler directives.

Segment start directives.

Al∞á 808╢ statement≤ mus⌠ bσ assigneΣ t∩ onσ oµ thσ fou≥ segment≤ ì
s∩á the∙á caεá bσ accesseΣ b∙á thσá CPU«á ┴á statemen⌠á directivσ ì
statement¼á CSE╟á DSEG,SSE╟ o≥ ESE╟ specifie≤ tha⌠ thσ statement≤ ì
followinτá i⌠ belonτ t∩ tha⌠ segment«á Thi≤ i≤ neccessr∙ s∩á tha⌠ ì
thσá assemble≥ caε providσ ß segmen⌠ over-ridσ prefi° iµá needed« ì
The statements are as follows.

CSEG      numeric exp.
CSEG
CSEG      $
Specifie≤á tha⌠á thσá followinτ statement≤á belonτá t∩á thσá Codσ ì
Segment« Thσ numeriπ expressioε fixe≤ thσ physica∞ addres≤ oµ thσ ì
segment¼á anΣá thσá codσá i≤ no⌠á relocatable«á Thσá seconΣá forφ ì
generate≤á relocatablσ code,anΣ i≤ useΣ wherσ thσ segmen⌠ addres≤ ì
i≤ no⌠ knowε a⌠ assembl∙ time« Thσ thirΣ forφ i≤ useΣ t∩ continuσ ì
a segment where it has been interrupted by another SEG directive.
DSEG      numeric exp.
DSEG
DSEG      $
Specifies that the following is assigned to the Data Segment.

SSEG      numeric exp.
SSEG
SSEG      $
Specifies that the following is assigned to the Stack Segment.

ESEG      numeric exp.
ESEG
ESEG      $
Specifies that the following is assigned to the Extra Segment.
ORG       numeric exp.
Set≤ thσ offse⌠ oµ thσ locatioε counte≥ iε thσ curren⌠ segmen⌠ t∩ ì
value of (numeric exp.)

IF and END IF

IF        numeric expression
          source line 1
          .
          .
          source line n
          ENDIF
Cause≤ conditiona∞ assembly.Iµ numeriπ expressioε i≤ non-zero,thσ ì
line≤á arσ assembled,iµ zer∩ the∙ arσ excluded.NesteΣ I╞á i≤á no⌠ ì
allowed.
INCLUDE        filename
Thi≤á include≤á anothe≥ 808╢ filσ iε thσ sourcσ text.Ma∙á no⌠á bσ ì
nested.File type defaults to .A86 .

END
Marks the end of the source file.(optional)

EQU
symbol    EQU       numeric exp.
                    address exp.
                    register
                    instruction nmemonic
The required symbol must not be terminated with a ":".
eg M EQU MOV
     M   AX,BX   ;assembles as MOV AX,BX
DB
Assign≤ storagσ areß iε bytσ format.Thi≤ i≤ thσ onl∙ storagσ typσ ì
to allow more than 2 bytes of a string.

DW
Assign≤á ▓á Bytσ word≤ oµ storage(lowes⌠ ╕ bit≤ storeΣ a⌠á lowes⌠ ì
address).

DD
Assign≤á ┤ byte≤ oµ storage(A≤ aε addres≤ storage,thσá offse⌠á i≤ ì
stored at the lowest word, the segment is stored at the highest).

RS
Reserves storage, but does not initialize it.
eg  BUFFER    RS     80h

RB(,RW)      numeric exp.
Reserves a number of bytes(,words),but does not initialize it.
TITLE       string const.
Prints up to 30 chars at top of each printout page in listing.

PAGESIZE     numeric exp.
Number of lines to a listing page( default 66)

PAGEWIDTH    numeric exp
Number of colomns in listing (default 120,unless direct,=79)

EJECT
Eject a page during printout.EJECT is printed on next page.

SIMFORM
Replace≤á ßá forφá feeΣ characte≥ b∙ thσ correc⌠ numbe≥á oµá linσ ì
feeds.

NOLIST and LIST
As usual
:Assembler Operators
THE 8086 Assembler operators falls into the following types.

arithmetic
logical
relational
segment over-ride
variable manipulators and creators

The following is the syntax of these operators.

SYNTAX              RESULT
          logical

a XOR b
a OR b
a AND b
NOT a               a=16 bit
          relational
a EQ b              FFFFh if a=b,0 otherwise
a LT b
a LE b
a GT b
a GE b
a NE b

          arithmetic
$                   current location,current segment.
a+b
a-b
a*b                 unsigned
a/b                 unsigned
a MOD b
a SHL b
a SHR b
+a
-a
          segment over-ride
ES:
SS:
CS:
DS:                 over-rides assembler choice

          variable manipulators,creators
SEG a               creates no.=segment value
OFFSET a            creates no.=offset within segment
TYPE a              creates no.=1,2 or 4 if type
                    is byte,word or dword
LENGTH a            creates no.=length of bytes
LAST a              creates no.=LENGTH-1,otherwise 0
a PTR b             creates type of a,attributes of b
.a                  creates variable with offset of a,
                    segment=current segment.

:Invocation of XASM86.COM

The cross assembler is run by the following.

XASM86 filename {$optional parameters}

where the filename is {D:}filename{.filetype}
D:,if specified is the drive name.
filetype is standard type,default to .A86
eg XASM86 B:TEST
would assemble a file B:TEST.A86

The assembler produces 3 output files, as follows.
filename.LST   contains listing of source
filename.SYM   contains all user defined symbols
filename.H86   contains HEX format listing

Thσá HE╪á forma⌠ listinτ i≤ eithe≥ DIGITA╠ RESEARC╚ (default⌐á o≥ ì
INTEL format(see below).
Optional Parameters:

Iε thσ following¼á A,B,C,─ specif∙ valiΣ filedrives¼á ╪ specifie≤ ì
CO╬ ,┘ specifie≤ LST¼ ┌ specifie≤ NUL(suppres≤ output)

A         source file device,followed by A,B,C,D,X,Y,Z

H         hex output file device,followed by A,B,C,D,X,Y,Z

P         list file device,followed by A,B,C,D,X,Y,Z

S         symbol file device,followed by A,B,C,D,X,Y,Z

F         format of hex file,followed by I(INTEL),D(DIGITAL)
eg XASM86 TEST $AD SZ

Assemblσ TEST.A8╢ oε drivσ D║á ¼ producσ TEST.LST anΣ TEST.H8╢ oε
the same drive, no output of TEST.SYM

eg XASM86 TEST $AD SZ FI
Same as above, but format of hex file is INTEL.

:Example listing ( with comments)

ASM86 VER 1.0   SOURCE: EXAMPLE.A86                                    PAGE   1


                         ; ASSEMBLED BY THE INSTRUCTIONS:
                         ;
                         ;XASM86 EXAMPLE $FI
                         ;
                         ;The following is an example of an 8086
                         ;assembly listing produced by the XASM86
                         ;cross-assembler.Where possible the listing
                         ;is provided with suitable comments to
                         ;highlight certain actions of the assembler
                         ;or the 8086 software.
                         ;
                         ;
    0010                         SSEG    10H     ;ACTUAL ADDRESS=100H
  0000                   BOTTOM  RW      40H     ;40 WORDS
  0080                   TOP     RW      0H      ;JUST A LABEL
    0020                         DSEG    20H     ;ADDRESS AT 200H
  0000 12                FRED    DB      12H     ;1 BYTE
  0001 34                TONY    DB      34H     ;ANOTHER BYTE
  0002 34 12             GEORGE  DW      1234H   ;1 WORD,STORED AS 3412H
  0004 80 00 10 00       LABEL   DD      TOP     ;ASSEMBLER PICKS SEG,OFFSET
  0008 45 58 41 4D 50 4C SOURCE  DB      'EXAMPLE STRING NUMBER 1'       ;TEXT
       45 20 53 54 52 49
       4E 47 20 4E 55 4D
       42 45 52 20 31
                         ;
    0030                         ESEG    30H     ;ADDRESS AT 300H
  0000                   DESTB   RB      40H     ;DESTINATION BYTES
  0040                   DESTW   RW      20H     ;DESTINATION WORDS
                         ;
    0040                         CSEG    40H             ;ADDRESS AT 400H
  0000 B8 10 00          START:  MOV     AX,SEG BOTTOM   ;SEGMENT ADDRESS
  0003 8E D0                     MOV     SS,AX           ;TO SEGMENT REGISTER
  0005 B8 80 00                  MOV     AX,OFFSET TOP   ;OFFSET IN SEGMENT
  0008 B8 80 00                  MOV     AX,LENGTH BOTTOM*TYPE BOTTOM
  000B 8B E0                     MOV     SP,AX           ;TO STACK POINTER
                         ;
                         ;The above section of code extracts the segment address of
                         ;the stack for SS .The offset of the top of stack is loaded
                         ;to the stack pointer,using two operators,giving the same result
                         ;(offset and length*type).The same procedure for the other
                         ;segment registers used should be done as follows.
                         ;Note that the values loaded are immediate values,and not
                         ;labels,and thus segment over-ride is not applicable.
                         ;
  000D B8 20 00                  MOV     AX,SEG LABEL
  0010 8E D8                     MOV     DS,AX
  0012 B8 30 00                  MOV     AX,SEG DESTB
  0015 8E C0                     MOV     ES,AX
                         ;
                         ;Now to test the type operands,byte/word mixture
                         ;
  0017 A1 02 00                  MOV     AX,GEORGE
                         ;
                         ;This is valid,since AX and GEORGE are words
** ERROR NO:  8"   OPERAND(S) MISMATCH INSTRUCTION
ASM86 VER 1.0   SOURCE: EXAMPLE.A86                                                                          PAGE   2


  001A 90 90 90 90 90 90         MOV     AX,FRED
                         ;
                         ;Invalid,since FRED is byte
                         ;
  0020 A1 00 00                  MOV     AX,WORD PTR FRED
                         ;
                         ;Valid,since WORD PTR over-rides byte description
                         ;for this case.
                         ;
                         ;Now we try string operations
                         ;
  0023 B9 17 00                  MOV     CX,LENGTH SOURCE/TYPE DESTB
  0026 BE 08 00                  MOV     SI,OFFSET SOURCE
  0029 BF 00 00                  MOV     DI,OFFSET DESTB
  002C F3 A4                REP  MOVS    DESTB,SOURCE
                         ;The operands must be used for the MOVS instruction
                         ;to allow the assembler to chose the byte or word
                         ;code,and to allow for segment over-ride where valid
                         ;
  002E B9 0C 00                  MOV     CX,LENGTH SOURCE/TYPE DESTW+1
  0031 BE 08 00                  MOV     SI,OFFSET SOURCE
  0034 BF 40 00                  MOV     DI,OFFSET DESTW
  0037 F3 A5               REP   MOVS    DESTW,WORD PTR SOURCE
                         ;
                         ;The word type of string move.
                         ;
  0039 26 8B 1E 40 00            MOV     BX,DESTW
                         ;
                         ;Assembler will generate segment over-ride prefix
                         ;to segment ES(=26H),or can generate yourself,
                         ;(usually error) as follows.
                         ;
  003E 36 8B 1E 40 00            MOV     BX,SS:DESTW

  END OF ASSEMBLY. NUMBER OF ERRORS:   1