Comment by iam-TJ | Hacker News Reader

Comment by iam-TJ | Hacker News Reader

I've still got the original Sinclair ZX81 bought in March 1981 (but not delivered until 1st week of June 1981 due to demand) and it still works, even with its wobbly 16KiB RAM Pack!

Much fun was had programming in machine language by looking up op-codes in Rodney Zak's "Programming the Z80" and counting the clock cycles to figure out the most efficient set of op-codes. As I recall the fastest op-code requires 4 clock cycles but some instructions would need more than 10 so much performance could be gained by knowing and optimising. This was before there was a Z80 assembler available so the hex of those op-codes had to be typed and POKEd into memory from the BASIC interpreter.

A side-note - don't forget the ZX81 was preceded by the Sinclair ZX80 in 1980 [0].

FYI, the retro community have developed an internal 16Kb 'daughter board' so you can finally ditch that unreliable wobbly ram pack.

Also, there's a 'composite mod' which replaces the RF modulator, and gives you rock solid composite image on modern TVs.

Modern TVs don't have a composite input. :)

It's a shame they didn't have SCART output.

I don't think that's actually true. Even my shiny new Sony 4K HDR TV, bought literally this year, has a single composite input.

It's certainly being phased out, but it's not gone yet.

My new Phillips 4K OLED does not, which I only discovered when I wanted to connect my https://en.wikipedia.org/wiki/C64_Direct-to-TV to it.

To explain further: The internal composite signal of the ZX81 (before it hits the RF modulator) has a poor "back porch"[1] signal, which prevents a lot of digital TVs from showing a steady image of the ZX81s screen. The composite mod for the ZX81 rectifies this, so the composite output can be feed into either a modern TV that still has a composite input, or an inexpensive composite-to-HDMI converter.

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[1] https://en.wikipedia.org/wiki/Horizontal_blanking_interval

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