)
Call VioReadCharStr with:
	STACK:	WORD	VIO handle (must be 00h)
		WORD	column at which to start reading
		WORD	row at which to start reading
		DWORD	pointer to WORD containing length of buffer in bytes
			on return, WORD contains number of bytes actually read
		DWORD	pointer to buffer for character string
Return: AX = error code (00h, 74h, 166h ,167h, 1B4h) (see #00373)