Halt Right There!

You ZX/TS users have been told, and told again, “Don’t mess with the interrupts” and “Never use the HALT command.” The severity of the admonitions seem to imply that a fate-worse-than-crashing awaits those who would tamper with such things. When HALT is encountered, the Z80 CPU stops running your program. In this way it is like the BASIC STOP command. More precisely, it endlessly executes NOPs (no operation) to keep memory refreshed.