Z80: the “User Manual” was already 300+ pages (:
Posted by jpluimers on 2014/08/14
Today yet another post in the series of BitSavers and History articles.
I already wrote a bit on the Z80 processor in XOR swap/exchange: nowadays an almost extinct means to exchange two distinct variables of the same size.
Popular Z80 powered computers were Amstrad CPC, MSX, Exidy Sorcerer, TRS-80, P2000, Sinclair ZX80, ZX81 and ZX Spectrum, Kaypro, Osborne 1 and the Z-80 SoftCard for Apple II.
The Z80 was widely popular in the 1980s as it could do more than the MOS 6502 of that time:
- The 6502 (see 6502.org) had
– only 56 instructions (the 65C02 variations had a few more), and the XOR was called EOR.
– addressing memory was limited (not all instructions understood both zero-page-absolute and absolute addressing)
– only 3 registers (A, X and Y)- The Z80 (see z80.info) had:
– only 68 instructions and XOR was indeed called XOR
– many more addressing modes than the 6502
– a whopping 9 registersStill the XOR swap algorithm was used a lot back then because of register pressure in the Z80.
Compared to current processors you’d think the Z80 was so small that a few pages of documentation would suffice.
Not so: back then they had a truckload of documentation and it would all be on paper (PDF ame in 1993 and it took quite a while to become popular).
Some of the Z80 documentation has found its way to BitSavers.org:
- The Z80 Data Book (which originates in the 1980s) is already 100+ pages
- And more recently (2004! the Z80 is still used a lot in embedded systems today), the Z80 Family CPU User manual is a whopping 300+ page book
–jeroen
The Wiert Corner - irregular stream of stuff 
Leave a comment