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                           TSM_RDME.TXT
                        TURBO ASSEMBLER 4.0

This file contains information on:
  1) Assembling and linking with TASM 4.0
  2) The PUSHSTATE and POPSTATE directives
  3) Text equate substitution
  4) Rotate instruction extension for 8086


1. Assembling and linking with TASM 4.0
=======================================
  The TASM 4.0 package includes three different assemblers:

    TASM.EXE           16-bit real-mode assembler
    TASMX.EXE          16-bit protected-mode assembler
    TASM32.EXE         32-bit protected-mode assembler

  All three assemblers are capable of producing both 16- and 32-bit
  object files, depending on the directives contained in your assembler
  source files. If you produce a 16-bit object file, then you must use
  the 16-bit linker (TLINK.EXE) to link your application. If you produce
  a 32-bit object file, then you must use the 32-bit linker (TLINK32.EXE)
  to link your application.

  TASM.EXE is a real-mode assembler, meaning that it is capable of using
  only the lower 640K of memory addressable by DOS. If you're assembling
  larger applications, use either TASMX.EXE or TASM32.EXE. Both of these
  assemblers use the DPMI server to take advantage of extended memory.

  The biggest difference between the three assemblers is the type of
  debug information they produce when you assemble your source files with
  the /zi command-line option. Both TASM.EXE and TASMX.EXE produce
  only 16-bit debug information. TASM32.EXE produces only 32-bit debug
  information. If you plan to use Turbo Debugger to debug your assembler
  application, then you must assemble 16-bit files with either TASM.EXE
  or TASMX.EXE. To produce 32-bit debug information, then you must assemble
  your files with TASM32.EXE.


2. PUSHSTATE and POPSTATE directives
====================================

  The PUSHSTATE directive saves the current operating state on an
  internal stack that is 16 levels deep. PUSHSTATE is particularly
  useful if you have code inside a macro that functions independently
  of the current operating state, but does not affect the current
  operating mode.

  The state information that Turbo Assembler saves consists of:

  o  The current emulation version (for example T310)
  o  The mode selection (for example IDEAL, MASM, QUIRKS, MASM51)
  o  EMUL or NOEMUL switches
  o  The current processor or coprocessor selection
  o  MULTERRS or NOMULTERRS switches
  o  SMART or NOSMART switches
  o  The current radix
  o  JUMPS or NOJUMPS switches
  o  LOCALS or NOLOCALS switches
  o  The current local symbol prefix

  Use the POPSTATE directive to return to the last saved state
  from the stack.

; PUSHSTATE and POPSTATE example

.386
ideal
model small
dataseg

pass_string db 'passed',13,10,36
fail_string db 'failed',13,10,36

codeseg

jumps

        ; Show changing processor selection, number radix, and JUMPS mode

        xor     eax,eax    ; Zero out eax. Can use EAX in 386 mode
        pushstate          ; Preserve state of processor, radix and JUMPS

        nojumps
        radix   2          ; Set to binary radix
        p286

        mov     ax,1       ; Only AX available now. EAX would give errors.
        cmp     ax,1
        jne     next1      ; No extra NOPS after this
                           ; Assemble with /la and check in .lst file.
        mov     ax,100     ; Now 100 means binary 100 or 4 decimal.
next1:
        popstate           ; Restores JUMPS and 386 mode and default radix.

        cmp     eax,4      ; EAX available again. Back in decimal mode.
        je      pass1      ; Extra NOPS to handle JUMPS. Check in .lst file
        mov     dx,OFFSET fail_string    ; Load the fail string
        jmp     fini
pass1:
        mov     dx,OFFSET pass_string    ; Load the pass string.
fini:
        mov     ax,@data   ; Print the string out
        mov     ds,ax
        mov     ah,9h
        int     21h

        mov     ah, 4ch    ; Return to DOS
        int     21h
end


3. Text Equate Substitution
===========================
TASM 4.0 has changed the way text equates are substituted since the TASM 3.0
version. This makes some TASM 3.0 code produce errors when assembled with
TASM 4.0. To remedy this problem, do one of the following:

  1) Use the /UT300 command line directive to select TASM 3.0 style
    processing.

  2) Explicitly use the % text macro substitution operator at the
     start of lines that cause errors with TASM 4.0.


4) Rotate instruction extension for 8086
========================================
TASM 4.0 permits rotation instructions to have a constant value other
than 1 when an 8086 processor is selected. TASM accomplishes this by
emitting the appropriate number of single rotate instructions when the
8086 processor is selected.

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