Format of Econet control block:
Offset	Size	Description	)
 00h	DWORD	-> command block (see #03038)
 04h	WORD	length of transmit data block
 06h	DWORD	-> transmit data block
 0Ah	WORD	length of reply block (set to 0000h prior to call)
 0Ch	DWORD	-> reply block
 10h	WORD	return code (set to 0000h prior to call) (see #03037)
 12h	DWORD	reserved for Econet use