Editing ZX80 (section)

== Hardware ==
[[File:ZX80 platine.jpg|thumb|Inside the ZX80: Z80 is large chip in center. 4K ROM is medium-sized chip in upper right. 1K RAM is implemented by two chips in upper left. Video modulator is metal box at top.]]

Internally, the machine was designed by [[Jim Westwood]] around a [[Zilog Z80|Z80]] [[central processing unit]] with a [[clock speed]] of 3.25&nbsp;MHz, and was equipped with 1&nbsp;[[Kilobyte|KB]] of [[static RAM]] and 4&nbsp;KB of [[read-only memory]] (ROM). It had no sound output.<ref>{{cite book | url = https://ia600501.us.archive.org/14/items/the-zx80-companion/TheZX80Companion%282ndEd%29.pdf | title = The ZX80 Companion | last1 = Maunder | first1 = Bob | last2 = Trotter | first2 = Terry | last3 = Logan | first3 = Ian | date = 1980 | publisher = LINSAC | access-date = 29 Dec 2024 | language = en | pages = 7 | quote = The [television] set should be tuned to channel 36 UHF by means of the normal tuning controls. There is no sound output so the volume should be set to minimum.}}</ref>

The ZX80 was designed around readily available [[transistor-transistor logic|TTL]] ICs, without any custom chips; the only proprietary technology was the [[firmware]].<ref>{{cite web | url = https://www.8bity.cz/files/zx80const.pdf | title = Sinclair ZX80 assembly instructions | author = Sinclair Research Ltd.  | date = 1980 | website = Martinův 8-bitový blog | access-date = 29 Dec 2024 | language = en | pages = 7-8 }}</ref><ref>{{cite book | url = https://ia600501.us.archive.org/14/items/the-zx80-companion/TheZX80Companion%282ndEd%29.pdf | title = The ZX80 Companion | last1 = Maunder | first1 = Bob | last2 = Trotter | first2 = Terry | last3 = Logan | first3 = Ian | date = 1980 | publisher = LINSAC | access-date = 29 Dec 2024 | language = en | pages = 90 }}</ref>

The machine was mounted in a small white plastic case, with a one-piece blue [[membrane keyboard]] on the front. There were problems with durability, reliability and overheating (despite appearances, the black stripes visible on the top rear of the case are merely cosmetic, and are not ventilation slots).<ref>{{cite magazine |last=Tebbutt |first=David |date=April 1980|title=Benchtest: The Sinclair ZX80 |url=https://archive.org/details/PersonalComputerWorld1980-04 |magazine=[[Personal Computer World]]|pages=55|access-date = 29 Dec 2024|quote=…the casing even has go-faster stripes, which look suspiciously like ventilation slots in black and white photographs (coincidence, I'm sure).}}</ref>

Video output was black-and-white, character-based.{{r|mccallum198101}} However, the [[ZX80 character set]] included some simple block-based graphics glyphs, allowing basic graphics to be accomplished, with some effort. One advantage to using monochrome video is that different colour broadcast standards (e.g. [[PAL]], [[SECAM]]) simply weren't an issue when the system was sold outside the UK.<ref>{{cite magazine |last=Tebbutt |first=David |date=April 1980|title=Benchtest: The Sinclair ZX80 |url=https://archive.org/details/PersonalComputerWorld1980-04 |magazine=[[Personal Computer World]]|pages=55|access-date = 29 Dec 2024|quote=American television (525 line) users are catered for as well; all they need to do is solder in one diode and the system is converted from 50 to 60Hz standards.}}</ref>

Display was over an [[radio frequency|RF]] [[RF connector|connection]] to a household [[television]], and simple offline program storage was possible using a [[cassette deck|cassette recorder]]. The video display generator of the ZX80 used minimal hardware plus a combination of software to generate a video signal. (Some say this was an idea popularised by [[Don Lancaster]] in his 1978 book [[TV Typewriter#TV Typewriter Cookbook|''The TV Cheap Video Cookbook'']] and his "[[TV Typewriter]]".<ref>{{ cite book | chapter-url = https://www.nvg.ntnu.no/sinclair/computers/zx80/zx80_sst.htm | chapter = A New Means To An Old End | title = Sinclair and the 'Sunrise' Technology | last = Adamson | first = Ian | author2 = Richard Kennedy | publisher = [[Penguin Books]] | year = 1986 }}</ref> However, that design didn't involve a microprocessor for video generation, and it wasn't really similar to the ZX80 in other aspects either. The ZX80 and ZX81 also employed very specific traits of the Z80 processor.)

Unlike the later follow up, ZX81, the ZX80 could only generate a picture when it was idle, i.e. waiting for a key to be pressed. When running a BASIC program, or when pressing a key during editing, the tv-display would therefore blank out (lose synchronisation) momentarily while the processor was busy. So a BASIC program had to introduce a pause for input to display the next change in graphical output,{{r|mccallum198101}} making smooth moving graphics impossible. This could be overcome only by very clever machine code tricks. These had to effectively replace the video rountines in ROM and embed the same in the normal program logic with exact timing, which is extremely cumbersome. However, a few such games were developed by skilled users or programmers later on.