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Man Pages

Manual Reference Pages  -  AS31 (1)


as31 - An Intel 8031/8051 assembler




as31 [ -Fformat ] [ -Aarg ] [ -l ] infile.asm


As31 assembles infile.asm into one of several different output formats. The output will be in a file called infile.obj. The .asm extenstion is required.


The options must appear before the input file name. Both options are optional. The text of each flag must appear on the same argument as the flag. For example, "-Fod" is a valid argument, but "-F od" is not.
-Fformat This options specifies the output format that is to be used.
Currently the only options available for this are:
hex This format is the Intel HEX format which is expected by a number of EPROM programmers and the PAULMON debugger. For use with some programmers, the output file’s extension may have to be changed to .HEX to be recognized by the programmer. No -A option is used. This format should be the default if no -F option is used.

tdr This format generates an asci file of hex digits formatted in such a way, so that they can be read by tdr’s debugger. An argument can be specified (See -A option) which will pass a format specific string to the format generator. In this case, the argument string represents an offset to add to the location counter. This offset is specified in decimal and defaults to 64*1024 (0x10000). To specify and offset of 100, you would need "-Ftdr -A100" when invoking the assembler.

byte This format is simply an address and a byte on each line, in ascii. No -A option is used.

od This format is similar to the output from od(1). The format consists of an address followed by sixteen hexadecimal bytes, followed by the equivilant ASCII. No -A option is used.

srec2, srec3, srec4 The srecord generator is capable of generating output with any one of 2, 3, or 4 byte addresses. The -A option can be used to set the base address offset, the default here is 0x0000 (unlike tdr).
NOTE: This assembler allows for the output formats to be expanded to include many different output formats.
-Aarg This option specifies a format specific string which is passed to the format generator. Both format "tdr" and the srecord formats use this option.
-l This option tells the assembler to also generate a listing file. A listing will be placed in the file infile.lst. Where ’infile’ is the file that is being assembled. This option may appear anywhere before infile.asm. The option must occur isolated on the command line.
The listing file shows the assembler generated code in hex, and up to 60 characters are retained from the source file.
-cgi This option instructs the assembler to supress the listing, output the object code to stdout, and DELETE the original assembly source file. This is intended to be used with a cgi script which builds a custom cunfigured temporary copy of an assembly source. This option should not normally be used.


This assembler accepts standard 8031/8051 instruction formats. Below is a list of instructions and addressing modes.

INSTRUCTION                             BYTES     CYCLES
-----------                             -----     ------
ACALL     addr11                        2         24
ADD       A, #data8                     2         12
ADD       A, @Ri                        1         12
ADD       A, Rn                         1         12
ADD       A, direct                     2         12
ADDC      A, #data8                     2         12
ADDC      A, @Ri                        1         12
ADDC      A, Rn                         1         12
ADDC      A, direct                     2         12
AJMP      addr11                        2         24
ANL       A, #data8                     2         12
ANL       A, @Ri                        1         12
ANL       A, Rn                         1         12
ANL       A, direct                     2         12
ANL       C, /bit                       2         24
ANL       C, !bit                       2         24
ANL       C, bit                        2         24
ANL       direct, #data8                3         24
ANL       direct, A                     2         12
CJNE      @Ri, #data8, rel              3         24
CJNE      A, #data8, rel                3         24
CJNE      A, direct, rel                3         24
CJNE      Rn, #data8, rel               3         24
CLR       A                             1         12
CLR       C                             1         12
CLR       bit                           2         12
CPL       A                             1         12
CPL       C                             1         12
CPL       bit                           2         12
DA        A                             1         12
DEC       @Ri                           1         12
DEC       A                             1         12
DEC       DPTR                          1         12
DEC       Rn                            1         12
DEC       direct                        2         12
DIV       AB                            1         48
DJNZ      Rn, rel                       2         24
DJNZ      direct, rel                   3         24
INC       @Ri                           1         12
INC       A                             1         12
INC       DPTR                          1         24
INC       Rn                            1         12
INC       direct                        2         12
JB        bit, rel                      3         24
JBC       bit, rel                      3         24
JC        relative                      2         24
JMP       @A + DPTR                     1         24
JMP       @DPTR + A                     1         24
JNB       bit, rel                      3         24
JNC       relative                      2         24
JNZ       relative                      2         24
JZ        relative                      2         24
LCALL     addr16                        3         24
LJMP      addr16                        3         24
MOV       @Ri, #data8                   2         12
MOV       @Ri, A                        1         12
MOV       @Ri, direct                   2         24
MOV       A, #data8                     2         12
MOV       A, @Ri                        1         12
MOV       A, Rn                         1         12
MOV       A, direct                     2         12
MOV       C, bit                        2         12
MOV       DPTR, #data16                 3         24
MOV       Rn, #data8                    2         12
MOV       Rn, A                         1         12
MOV       Rn, direct                    2         24
MOV       bit, C                        2         24
MOV       direct, #data8                3         24
MOV       direct, @Ri                   2         24
MOV       direct, A                     2         12
MOV       direct, Rn                    2         24
MOV       direct, direct                3         24
MOVC      A, @A + DPTR                  1         24
MOVC      A, @A + PC                    1         24
MOVC      A, @DPTR + A                  1         24
MOVC      A, @PC + A                    1         24
MOVX      @DPTR, A                      1         12
MOVX      @Ri, A                        1         24
MOVX      A, @DPTR                      1         24
MOVX      A, @Ri                        1         24
MUL       AB                            1         48
NOP                                     1         12
ORL       A, #data8                     2         12
ORL       A, @Ri                        1         12
ORL       A, Rn                         1         12
ORL       A, direct                     2         12
ORL       C, /bit                       2         24
ORL       C, !bit                       2         24
ORL       C, bit                        2         24
ORL       direct, #data8                3         24
ORL       direct, A                     2         12
POP       direct                        2         24
PUSH      direct                        2         24
RET                                     1         24
RETI                                    1         24
RL        A                             1         12
RLC       A                             1         12
RR        A                             1         12
RRC       A                             1         12
SETB      A                             1         12
SETB      bit                           2         12
SJMP      relative                      2         24
SUBB      A, #data8                     2         12
SUBB      A, @Ri                        1         12
SUBB      A, Rn                         1         12
SUBB      A, direct                     2         12
SWAP      A                             1         12
XCH       A, #data8                     2         12
XCH       A, @Ri                        1         12
XCH       A, Rn                         1         12
XCH       A, direct                     2         12
XCHD      A, #data8                     2         12
XCHD      A, @Ri                        1         12
XCHD      A, Rn                         1         12
XCHD      A, direct                     2         12
XRL       A, #data8                     2         12
XRL       A, @Ri                        1         12
XRL       A, Rn                         1         12
XRL       A, direct                     2         12
XRL       direct, #data8                3         12
XRL       direct, A                     2         12


As31 includes the following assembler directives:
.ORG expr Start assembling at the address specified by the expression expr. An error occurs if the assembler starts assembling over an address space that has previously been assembled into.

.EQU symbol, expr Set symbol to the value of expr. The value for expr must be known during the first pass, when the line containing the .EQU is encountered.

.BYTE expr, expr, ... Assemble the bytes specified by the expression into memory. A string may also be specified with this directive.

.WORD expr, expr, ... Assemble the words specified by the expression into memory. The byte ordering used, is that used by the 8031.

.FLAG symbol1, symbol.[0-7] Sets symbol1 to the bit address specified by the symbol.[0-7] expression. Where [0-7] denotes a character between 0 and 7. The resulting bit address is checked to see if it is a valid bit address.

.END This directive is ignored.

.SKIP expr Adds the value of expr to the location counter. Used to reserve a block of uninitialized data. Expr should be in bytes.


- All characters following a semi-colon are ignored until a newline is encountered.

- All numbers default to decimal, unless the number starts with one of the following:
0x or 0X This indicates a hexadecimal number. ie. 0x00ff
0b or 0B This indicates a binary number. (1’s and 0’s). ie. 0b1100110010
0 This indicates an octal number. ie. 0377
- All numbers default to decimal, unless the number ends with one of the following characters:
b or B This indicates a binary number. Unless 0x was used above. ie. 1010101b
h or H This always indicates a hex number, However the if the first character is non-numerical, then either 0x or 0 must be specified. This avoids confusing the assembler into thinking a hex number is a symbol. For example: 0ffh, 0xffh, 0XffH, 20h, 0x20 and 020h are means to specify a valid hexdigit. But the following are not: ffh, 0ff.
d or D This forces a number to decimal. Unless 0X was used. ie. 129d
o or O This causes the number to be interpreted as octal. ie. 377o

- A character constant can be entered as ’c’ where c is some character. \b, \n, \r, \t, #146; \0 are also valid. A character constant can be used anywhere that an integer value can.

- A string is entered as a set of characters enclosed in double quotes "". A string is only valid with the .BYTE directive. \b, \n, \r, \t, \" are also valid escapes. However \0 is not.

- Instructions, directives, and the symbols: R0, R1, R2, R3, R4, R5, R6, R7, A, AB, and C can be entered in upper or lower case without assembler confusion. These words however cannot be defined as a user symbol. Any user symbol may be used, and case will be preserved. So the user symbols "foo" and "Foo" are different, but "addc" is the same as "aDdC".

- A symbol can be any alpha numerical character plus the underscore (’_’).

- Expressions are accepted in most places where a value or a symbol is needed. An expression consists of the following operators. All operators evaulate to integer objects (higher precedence opertors listed first):
- Unary minus
& Bit-wise AND.
| Bit-Wise OR.
* Integer multiplication.
\ Integer division
% Intieger modulus
+ Integer addition.
- Integer subtraction.
- In addition to these operators, a special symbol ’*’ may be used to represent the current location counter.


Below is a sample assembly program.

.org 0 start: mov P3, #0xff ; use alternate fns on P3                                          ; leds on P1 are inverted. setb F0 ; climbing up mov A, #0x01 ; initial bit

write: cpl A ; write it mov P1, A cpl A acall delay jb F0, climbup ; climbing which way?

climbdn: rr A ; down - shift right jnb ACC.0, write ; back for more setb F0 ajmp write

climbup: rl A ; up - shift left jnb ACC.7, write ; back for more clr F0 ajmp write .end                              ; this directive ignored.


Ken Stauffer (University of Calgary)
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