Sherlock: Routine at 50179

50179: Set The Printer Motor Speed Via Port 251

Used by the routine at 50148. The game's copy of the ROM COPY_LINE code: writes 2 to port 251 when the count in B is below three (slowing the printer motor for the last two pixel lines), and 0 otherwise, then waits until a read from that port comes back negative.
SetPrinterMotorSpeed	50179	LD A,B	Compare B with 3 and leave 255 in A when the count is below.
	50180	CP 3
	50182	SBC A,A
	50183	AND %00000010	Keep just bit 1, giving 2 (slow the printer motor) when the count is below three and 0 otherwise.
	50185	OUT (251),A	Send that strobe to the ZX Printer on port 251.
	50187	LD D,A	Keep the motor value just sent in D.
SetPrinterMotorSpeed_0	50188	IN A,(251)	Read port 251 and return if the ZX Printer is busy.
	50190	ADD A,A
	50191	RET M
	50192	JR NC,SetPrinterMotorSpeed_0	Go back to SetPrinterMotorSpeed_0 while the ZX Printer is not ready.
	50194	JP 3858	Jump to COPY_LINE at 3858.