The ZX Spectrum was a British computer produced by Sinclair Research in the 80's, The processor is a z80 produced by Zilog, still in production and has some interesting features, such as being a Von Neumann architecture it support self modifying code. The ROM on the ZX Spectrum includes a version of BASIC, but the device can also be programmed in assembler.
|high 8bit||low 8bit|
a is 8 bit accumulator hl is sort of a 16 bit accumualtor (only destination for 16bit add) b conventionally for loops : djnz is “decrement b, jump if not zero”
ld 'loads' right to left:
16bit pairs, bc, de, hl, ix, iy
push/pop stack - 16bits, eg:
arithmetic: inc, dec, add, sub, adc, sbc
wierd block processing instructions, ld, as in load, i/d inc/dec, r for repeat. each one uses bc,de and hl - bc is counter, de destination, hl source.
LD DE,0000h LD HL,4000h LD BC,0100h LDIR
copies 0x100 bytes of data from 0x4000 to 0x0000.
cpir is for searching memory, bc = counter, hl = source and a is the search value
LD HL,0000h LD BC,0000h LD A,124 CPIR