Sinclair ZX81 Operation & User’s Manual

The letters, digits, punctuation marks & so on that can appear in strings are called characters, & they make up the alphabet, or character set, that the ZX81 uses. Most of these characters are single symbols, but there are sone more, called tokens, that represent whole words, such as PRINT, STOP, **, & so on. There are 256 characters altogether, & each one has a code between 0 & 255. There is a complete list of them in appendix A. To convert between codes & characters, there are two functions, CODE & CHR$. CODE is applied to a string, & gives the code of the ...

This is the complete ZX80 character set, with codes in decimal & hex. If one imagines the codes as being Z80 machine code instructions, then the right hand columns give the corresponding assembly language mnemonics. As you are probably aware if you understand these things, certain Z80 instructions are compounds starting with CBh or EDh; the two right hand columns give these. Code Character Hex Z80 assembler - after CBh - after EDh 0 space 00 nop rlc b 1 01 ld bc,NN rlc c 2 02 ld (bc),a rlc d 3 03 inc bc rlc e 4 04 inc b rlc h 5 05 dec b rlc l 6 06 ld b,N rlc (hl) ...

40 LET C$=A$ 50 LET A$=B$ 60 LET B$=C$ 70 PRINT A$;" ";("<" AND A$

. This means 'message complete', or 'all right, computer, lets see some action'. The computer will now read the message, work out what has to be done, and do it. In this case, the screen will change to 4 is the answer - but of course you do not need to buy a computer to work that out. 0/0 (Note how zero is written with a slash to distinguish it from capital O. This is fairly common in computing circles.) is the report in which the computer tells you how it got on. The first 0 means 'OK, no problems'. (In appendix B the ...