From ba7c4ede344ab951599f10d06156a5f392fc4fb6 Mon Sep 17 00:00:00 2001 From: mahjongg2 Date: Mon, 7 Sep 2020 04:01:14 +0200 Subject: [PATCH] Create README.md --- README.md | 13 +++++++++++++ 1 file changed, 13 insertions(+) create mode 100644 README.md diff --git a/README.md b/README.md new file mode 100644 index 0000000..ea9acd8 --- /dev/null +++ b/README.md @@ -0,0 +1,13 @@ +# ZX81plus38 +Mij latest ZX81 clone without ULA built from discrete pin through hole components +It features a PCB with the exact same size as a normal ZX81, and features drill holes and connectors at the same locations (with the 3.5mm power jack replaced +with a modern Type B power jack, so you can power this ZX81 clone with a simple USB power supply, and with the RF output modulator replaced with a composite video +output connector, that produces a video signal that modern composire monitors should be able to accept (yes with a real fron porch signal). +There is no ULA needed for this clone, as all the ULA logic is replicated with modern DIP compatible logic IC's. The software (ZX-81 BASIC) first into a cheap OTP +(one time programmable) 27C256 ROM, and the bit-foor bit same code as a real ZX-81 code can be programmed into a 27C256 OTP ROM, but with a few jumper changes you +can alos use an original 8K ZX81 ROM. +Its also possible to fit several (different) code images into the ROM, and add switches to select one to boot with. +Extra logic was added to simulate the same cassette loading screen patterns as a real ZX81 has. +The cassette loading input logic has been eenhanced to give perfect cassette loading behaviour, even whith cassette signals generated with a laptop, for easy cassette loading. +The ULA replacement logic is ferfect enough to enable the use of games which use various enhanced highres graphics techniques to work flawlessly. +In fact the ZX81+38 clone is easy to build, and a joy to use.