INMC News

  

February/March 1980, Issue 6











Page 7 of 38











SOFT SPOTS

By Richard Beal (and others)

This tip presupposes that you are a person who assembles machine code in HEX, in memory, and then wants to convert it to DATA statements for use as machine code subroutines with the 8K BASIC. Assuming Nas-sys is in use, try this:

Assemble the machine code routines, in HEX, at the correct location in memory (and perhaps try them if possible). Go into BASIC (making sure that the free memory space does not overwrite the machine code routines). Then use the following command:

WIDTH 40:FOR A = B TO C STEP 2:PRINT DEEK(A);:NEXT

Where B is the start address in decimal, and C is the end address. The BASIC will print a series of numbers, stopping well short of the right hand edge of the screen. Using the Nas-sys edit commands, edit in line numbers and commas, and the job is done. No mistakes through trying to calculate the decimal equivalents of the HEX, or through copying the numbers wrong. What’s more the data is in double byte form, which may be loaded down using DOKE commands, taking half the time that it would take to POKE the data down.

Suppose you want to test to see if one of the 16 bit registers HL, DE or BC is zero. For example, this could be at the end of a loop that was counting down. A version of this in a magazine had the following:

    DEC DE
    LD A, D
    OR A
    JR NZ LOOP
    LD A, E
    OR A
    JR NZ LOOP

It would be a lot easier to put:

    DEC DE
    LD A, D
    OR E
    JR NZ LOOP

Suppose you want to jump to a certain address in your program, and that this address is currently stored in the HL register. You can just code;

    JP (HL)

This works very well.

Now suppose that you need to have set HL to a certain value when the jump is made. The method above is useless because HL can’t be at two different values at once. So code:

    LD HL, value of HL
    PUSH HL
    LD HL, address to jump to
    EX (SP), HL
    RET

or:


This is an OCR’d version of the scanned page and likely contains recognition errors.











Page 7 of 38