If HL = DE, the 2 flag is set, otherwise it is reset.
If HL is greater than or equal to DE, the carry flag is
If HL is less than DE, the carry flag is set.
And it only takes four bytes!
2. Not everyone has realised that the Nascom monitor program
uses the Z80 restart instructions to provide some useful
features. Print String is an easy way of putting out
EF RST 28H
48 45 4C 4C 4F DEFM /HELLO/
00 DEFB 0
These seven bytes will make the message ‘HELLO’ be
displayed. Don’t forget to put the value 00 at the end
of the message, or the screen will fill up with the contents
of the rest of your program!
3. Have you wondered about the meaning of the characters
which hex values 00 to 1F give you on the screen? Each
one is, in fact, a picture which represents the equivalent
ASCII code. For example,
is a bell!
4. The breakpoint command uses a restart to stop the program
and display the registers. If you want, you can put the
same code, E7 in hex, in several places in your program.
You may find it a good idea to fill any empty space with
this code, because if you jump to it by mistake, the
program will stop, and the register display may give you
5. In case all this has been too easy, here is a puzzle for
AF XOR A Set A to 0
06 00 LD B,0 Set B to 0
3C LABL INC A Increment A
27 DAA Decimal adjust
10 FC DINZ LABL Repeat, 256 times.
E7 RST BRKPT Display registers.
Now A has been incremented 256 times, and the DAA instruction
makes this work in decimal, so A should be 56 at the end.
Why isn’t it, and how would you correct the program? (No,
the Z80 doesn’t have a fault in it!)
6. The original Nascom Software notes suggested jumping to an
/ .. ..