Quick Reference

The code that dgrdo / ASM recognises and compiles is composed of two large parts:

  1. Assembler directives
  2. Digirule Assembly

Assembler directives

  • .EQU

    Assigns an expression to a symbol. At the moment, .EQU is used to assign easy to remember names to constants. See for example the way the status_reg is defined in this example

  • .DB

    Sets the default value of one or more BYTE size memory locations.

    A straightforward example of its use is available here. Since .DB is most commonly used with Labels, see further below for more examples.

  • Labels

    A label is composed of alphanumeric characters and _. Labels cannot start with a number and are terminated by a colon (:).

    The most common use of a label is controlling the flow of code execution with a JUMP instruction, as is done here between lines 30 and 39

    Combined with the .DB directive, labels can be used to create and access "variables" at the lowest level. For more examples see Assignments.

  • Comments

    Anything preceded by a # character is considered a comment.

Digirule Assembly

This is only a brief reference of the instruction sets each Digirule model understands.

An extensive list of fully documented examples you can try out on dgrdo / ASM is available here.

Digirule 2A

Flow Control Memory Arithmetic Logic Other
HALT COPYLR ADDLA ANDLA NOP
DECRJZ COPYLA ADDRA ANDRA SPEED
INCRJZ COPYAR SUBLA ORLA INITSP
BCRSC COPYRA SUBRA ORRA
BCRSS COPYRR SHIFTRL XORLA
JUMP CBR SHIFTRR XORRA
CALL SBR DECR
ADDRPC INCR
RETLA RANDA
RETURN

Where:

  • L stands for Literal
  • R stands for Address
  • A stands for Accumulator (The only "register" in the Digirule CPU)
  • Z stands for Zero

For example:

  • COPYLA 2 Will set the Accumulator to 2
  • COPYLR 2 120 Will set memory address 120 to 2.
  • COPYRR 24 25 Will copy the value of memory address 24 to that of 25
  • COPYRA 120 Will set the Accumulator to whatever value is in address 120 and so on.

For a full reference, please see here.

Digirule 2U

The 2U version supports all 2A instructions plus the following:

Flow Control Memory Arithmetic Logic Other
JUMPI COPYLI MUL COMOUT
CALLI COPYRI DIV COMIN
BTSTSC COPYAI COMRDY
BTSTSS COPYIR
COPYII PINOUT
COPYRR PININ
SWAPRA PINDIR
SWAPRR
BCLR
BSET
BCHG

Where:

  • BTSTSC, BTSTSS are equivalent to BCRSC, BCRSS.

  • BCLR, BSET are equivalent to CBR, SBR.

  • 'I' stands for "Indirectly". In other words, where COPYRR 24 25 copied the value of address 24 to address 25, COPYII 24 25 performs a copy between the memory addresses that 24,25 point at.

    For example:

    COPYLR R0 R2 # Load R2 with the address of R0
COPYLR R1 R3 # Load R3 with the address of R1
COPYII R2 R3 # Copy indirectly from R2 to R3. In the end, R1 will receive the 5
HALT 
R0:
.DB 5
R1:
.DB 0
R2:
.DB 0
R3:
.DB 0

A more detailed version of this reference card is available here