Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear. It only takes a minute to sign up.
Sign up to join this community
I'm currently writing a ZX Spectrum emulator (I know there are plenty, but it's a project).
I'm having an issue where it keeps repeating the last key press even though I know the port lines have been reset.
This is what it looks like: ZXE Keyboard Shenanigans (in this recording, I pressed C once).
It might be helpful if I could know the location in memory where the Speccy stores lines of BASIC being entered, so I could see what's updating that.
It's all in the original ZX Spectrum user manual.
Chapter 24 'The Memory' details the various memory areas maintained by ZX BASIC, including the memory format of a BASIC line and of the various types of variables.
Chapter 25 'System Variables' lists the various system variables, some of which are the start addresses of the various memory areas.
16-bit start address of BASIC line being edited is stored in E_LINE at address 23641 (0x5C59).
16-bit end address of BASIC line being edited is WORKSP-1.
16-bit address WORKSP is stored at address 23649 (0x5C61).
You'll find the below diagram of memory allocation in chapter 24.
The keyboard subroutines move the last key that has been pressed into the system variable LAST_K ($5C08).
The KSTATE array (the 8 bytes before LAST_K, $5C00-5C07) are an array of two sets of 4-byte entries that are used for keyboard de-bounce and key repeat triggering.
