to an empty GO SUB stack.
		PUSH	BC	Next pass the 'error address'
		LD	(ERR-SP),SP	to the stack and save its
				address in ERR-SP.
		EX	DE,HL	An indirect return is now
		JP	(HL)	made to STMT-RET.
Note: When the routine is called from RUN the values of NEWPPC & NSPPC will have been affected and no statements coming after RUN can ever be found before the jump is taken.

THE 'GO SUB' COMMAND ROUTINE
The present value of PPC and the incremented value of SUBPPC are stored on the GO SUB stack.
1EED	GO-SUB	POP	DE	Save the address - STMT-RET.
		LD	H,(SUBPPC)	Fetch the statement number
		INC	H	and increment it.
		EX	(SP),HL	Exchange the 'error address'
				with the statement number.
		INC	SP	Reclaim the use of a location.
		LD	BC,(PPC)	Next save the present line
		PUSH	BC	number.
		PUSH	HL	Return the 'error address'
		LD	(ERR-SP),SP	to the machine stack and
				reset ERR-SP to point to it.
		PUSH	DE	Return the address -
				STMT-RET.
		CALL	1E67,GO-TO-1	Now set NEWPPC & NSPPC to
				the required values.
		LD	BC,+0014	But before making the jump
				make a test for room.

THE 'TEST-ROOM' SUBROUTINE
A series of tests is performed to ensure that there is sufficient free memory available for the task being undertaken.
1F05	TEST-ROOM	LD	HL,(STKEND)	Increase the value taken from
		ADD	HL,BC	STKEND by the value carried
				into the routine by the BC
				register pair.
		JR	C,1F15,REPORT-4	Jump forward if the result is
				over +FFFF.
		EX	DE,HL	Try it again allowing for a
		LD	HL,+0050	further eighty bytes.
		ADD	HL,DE
		JR	C,1F15,REPORT-4
		SBC	HL,SP	Finally test the value against the
				address of the machine stack.
		RET	C	Return if satisfactory.
Report 4 - Out of memory
1F15	REPORT-4	LD	L,+03	This is a 'run-time' error and the
		JP	0055,ERROR-3	error marker is not to be used.

THE 'FREE MEMORY' SUBROUTINE
There is no BASIC command 'FRE' in the SPECTRUM but there is a subroutine for performing such a task.
An estimate of the amount of free space can be found at any time by using:
'PRINT 65536-USR 7962'
1F1A	FREE-MEM	LD	BC,+0000	Do not allow any overhead.
		CALL	1F05,TEST-ROOM	Make the test and pass the