Format of AppleTalk control block:
Offset	Size	Description	)
 00h	WORD	command code (see #03255)
		OR with the following flags
		8000h start command then return
		4000h wait for interrupt service to complete
 02h	WORD	returned status
		0000h success (already initialized if func 01h)
 04h	DWORD	pointer to completion function
 08h	WORD	network number
 0Ah	BYTE	node ID
---if general func (01h,03h), control block continues:
 0Bh	BYTE	"inf_abridge"
 0Ch	WORD	"inf_config"
 0Eh	DWORD	pointer to buffer
 12h	WORD	buffer size
---if DDP function (20h-24h), control block continues:
 0Bh	BYTE	"ddp_addr_socket"
 0Ch	BYTE	"ddp_socket"
 0Dh	BYTE	"ddp_type"
 0Eh	DWORD	pointer to buffer
 12h	WORD	buffer size
 14h	BYTE	"ddp_chksum"
---if Name Binding Protocol (30h-34h), control block continues:
 0Bh	BYTE	"nbp_addr_socket"
 0Ch	WORD	"nbp_toget"
 0Eh	DWORD	pointer to buffer (see #03257)
 12h	WORD	buffer size
 14h	BYTE	"nbp_interval"
 15h	BYTE	"nbp_retry"
 16h	DWORD	"nbp_entptr"
---if AppleTalk Transaction Protocol (42h), control block continues:
 0Bh	BYTE	"atp_addr_socket"
 0Ch	WORD	"atp_socket"
 0Eh	DWORD	pointer to buffer
 12h	WORD	buffer size
 14h	BYTE	"atp_interval"
 15h	BYTE	"atp_retry"
 16h	BYTE	ATP flags
		bit 5: exactly one transaction
 17h	BYTE	"atp_seqbit"
 18h	BYTE	transaction ID
 19h  4 BYTEs	ATP user bytes
 1Dh	BYTE	number of BDS buffers
 1Eh	BYTE	number of BDS responses
 1Fh	DWORD	pointer to BDS buffers (see #03258)