## AS8X300 Assembler

####

       The  AS8X300 assembler supports the 8X300 and 8X305 microcon-
    trollers with the basic  syntax  of  the  MCCAP  Microcontroller
    Cross  Assembler  Program.   The  8x300 microcontroller has just
    eight basic instructions, MOVE, ADD, AND, XOR, XMIT,  NZT,  XEC,
    and  JMP.  The 8x305 has two addition instruction mnemonics, XML
    and XMR.  Three additional mnemonics are common to the 8X300 and
    8X305,  HALT, NOP, and SEL.  These five instructions are derived
    from the basic instructions.

       The  CALL and RTN functionalities are provided by macros con-
    tained in the s8xmcros.asm macro library.  These  functions  and
    others  in  the  library will be discussed in the following sec-
    tions.

####

    PROCESSOR SPECIFIC DIRECTIVES

    .8x300 Directive

    Format:

            .8x300

    The  default microcontroller selection is the 8x300.  The .8x300
    directive explicitly selects  coding  for  the  8x300  microcon-
    troller.

    .8x305 Directive

    Format:

            .8x305

    The  default microcontroller selection is the 8x300.  The .8x305
    directive explicitly selects  coding  for  the  8x305  microcon-
    troller.

    .liv Directive

    Format:

            .liv    sym     byte,bit,length

    The .liv declaration assigns a symbolic name to a left bank data
    field and defines the address (byte), position (bit), and preci-
    sion (length) of that variable.

    .riv Directive

    Format:

            .riv    sym     byte,bit,length

    The  .riv  declaration  assigns  a symbolic name to a right bank
    data field and defines the address (byte), position  (bit),  and
    precision (length) of that variable.

    .fdef Directive

    Format:

            .fdef   n(v),n(v),...

    The  .fdef  directive  is  used  to  specify  operand fields and
    default values for instruction extensions.   The  fields  define
    output  bit positions from MSB to LSB.  The directive may define
    up to 16 fields with a total length of 16 bits.  The  length  in
    bits  (n)  of each field is specified along with the an optional
    default field value (v) and an error checking flag (- preceeding
    n inhibits error checking).

    .xtnd Directive

    Format:

            .xtnd   [area]

    The option to output instruction extension code requires the de-
    finition of an extension field by .fdef and  the  invocation  of
    .xtnd with a defined area.  The generated extension code will be
    placed in the extended code area with the same  address  as  the
    assembled  instruction.  Invoking the .xtnd directive without an
    area will disable the extension code output.

####

    THE 8X300/8X305 MACRO LIBRARY

       The  macro  library,  s8xmcros.asm,  contains macros defining
    functionality not implemented directly into the assembler.

       The macros are:

            ORG     space, pgsize  ^/[...]/

            PROC    sub
            ENTRY   sub

            CALL    sub     ^/[...]/
            RTN     ^/[...]/

            CALL_TABLE      area_c, area_x  ^/[...]/

    Where  the ^/[...]/ syntax passes the string "[...]" as an argu-
    ment of the macro.

    ORG

    Format:

            ORG     space, pgsize   ^/[...]/

    The  ORG  macro changes the value of the location counter either
    conditionally or unconditionally.  The first  form  of  the  ORG
    macro:

            ORG     address

    unconditionally changes the value of the location counter to the
    value indicated by "address" which is any  constant,  symbol  or
    expression which evaluates to a value between 1 and 8191.

       The second form of the ORG macro conditionally sets the loca-
    tion counter to the next page or segment boundary if  there  are
    insufficient locations (space) in the current page (pgsize = 32)
    or segment (pgsize = 256).  If there is insufficient space  then
    a jump instruction is inserted pointing to the next page/segment
    boundary.

            ORG     space, pgsize  ^/[...]/

    The  optional  extended  code, [...], will be output if the jump
    instruction is inserted.

       If  "space" is equal to "pgsize", this statement is an uncon-
    ditional alignment to the next boundary of length "pgsize".

    PROC

    Format:

            PROC    sub

    The PROC macro creates the following code:

            .sbttl  sub:
    sub:

    ENTRY

    Format:

            ENTRY   sub

    The ENTRY macro creates the following code:

    sub:

    CALL, RTN, and CALL_TABLE

       The  macro  functions  CALL,  RTN, and CALL_TABLE implement a
    subroutine calling convention.  The 8X300/8X305 microcontrollers
    donot  have  a stack to save the return addresses for subroutine
    calling or subroutine returns.  The subroutine  calling  conven-
    tion  uses  register r11 as an index into a table of return jump
    addresses created by cooperation between the CALL macro and  the
    CALL_TABLE  macro.   The  CALL macro creates a unique return ad-
    dress symbol each time the macro  is  invoked.   The  CALL_TABLE
    macro creates the return jump table which is appended to the end
    of the assembled code.

    CALL

    Format:

            CALL    sub     ^/[...]/

    The CALL macro creates the following code:

            xmit    n,r11   [...]
            jmp     sub     [...]

    and  a  symbol, .rtn.n which points to the instruction following
    the inserted code, where n is 0 for the  first  CALL  invocation
    and  is  incremented  by  1 for each successive CALL invocation.
    The extended instruction code, [...], is optional.

    RTN

    Format:

            RTN     ^/[...]/

    The RTN macro creates the following code:

            jmp     .tbgn.  [...]

    where  .tbgn.   is  a label created by the macro CALL_TABLE when
    invoked at the end of the assembly.   The  table  return  index,
    r11,  will  select the proper return jump address entry from the
    jump table created by the CALL_TABLE macro.   The  extended  in-
    struction code, [...], is optional.

    CALL_TABLE

    Format:

            CALL_TABLE      area_c,area_x   ^/[...]/

    'area_c'  specifies the code area where the return jump table is
    to be placed.  'area_x' specifies the code area where the exten-
    sion  data  is  to be placed.  CALL_TABLE can be invoked with no
    arguments to use the current code and extension  areas  and  the
    default extended code.  To create an empty argument use the con-
    struct ^// for the argument.

       The CALL_TABLE macro creates an entry for each CALL macro in-
    voked in the assembly program and produces the following code:

            xec     .+1(r11) [...]
            jmp     .rtn.0  [...]
            jmp     .rtn.1  [...]
            jmp     .rtn.2  [...]
            ... repeating for the
                total number of CALLs

####

    8X300 AND 8X305 REGISTER SETS

    The following is a list of the 8X300 and 8X305 registers used by
    AS8X300:

        Registers Common To The 8X300 and 8X305
            r0,r1,r2,r3     -       8-bit registers
            r4,r5,r6,r7
            r10,r11
            aux (= r0)
            ivl (= r7)
            ovf (= r10)
            ivr (= r17)

        Additional Registers Of The 8X305
            r12,r13,r14,    -       8-bit registers
            r15,r16

        Register names containing multiple letters
        must be all lower case or all upper case.

####

    8X300 AND 8X305 INSTRUCTION SETS

       The  following  tables  list  all  8X300  and 8X305 mnemonics
    recognized by the AS8X300 assembler.  The following list  speci-
    fies the format for each addressing mode supported by AS8X300:

        Instruction Argument Syntax:

            op      instruction mnemonic

            reg     8X300/8X305 registers

            s       source I/O data feild
                    register, .liv or .riv symbol, or constant

            d       desination I/O data feild
                    register, .liv or .riv symbol, or constant

            exp8    8-bit value

            exp5    5-bit value

            df      I/O data field (may be optional)

            len     I/O field length (may be optional)

            r       bit positions to rotate (may be optional)

            addr    call or jump address or label

            code    extension field patterns (optional)

    The terms reg, s, r, exp8, exp5, df, len, addr, and code may all
    be expressions.

       Note  that  not  all addressing modes may be valid with every
    instruction.  Refer to the 8X300/8X305 technical data for  valid
    modes.

####

    Basic 8X300 and 8X305 Instructions
        MOVE, ADD, AND, XOR - Data Manipulation
            op      s,d             [code]
            op      s(r),d          [code]
            op      s,len,d         [code]

        XMIT - Load Immediate
            XMIT    exp8,reg        [code]
            XMIT    exp5,df,len     [code]

        XDEF - Execute
            XEC     exp8(reg),size          [code]
            XEC     exp5(df,len),size       [code]

        NZT - Non-Zero Transfer
            NZT     reg,exp8        [code]
            NZT     df,len,exp5     [code]

        JMP - Unconditional Jump
            JMP     addr    [code]

    Aditional 8X305 Instructions
        XML, XMR - Load Immediate To Left Or Right Bank
            op      immed   [code]

    Common Derived Instructions
        SEL, HALT, NOP - Derived Instructions
            SEL     df      [code]
            HALT            [code]
            NOP             [code]

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###### Last Updated: March 2025