OEL TTX2000 Issue 2.3: Routine at 1512

1512: pause_3s: Pause for 3 seconds

Used by the routines at downloader_not_present and display_error.
pause_3s	1512	PUSH BC	Preserve B.
	1513	EI	Enable interrupts.
	1514	LD B,$96	Set B to 150 as loop counter.
pause_3s_0	1516	HALT	Halt until next interrupt and loop.
	1517	DJNZ pause_3s_0	Halt until next interrupt and loop.
	1519	DI	Disable interrupts, restore value of B, and return.
	151A	POP BC
	151B	RET