Packet Format For Pad Mode; Using Pad Mode Pad Messages - Allen-Bradley 1779-KFMR User Manual

Chapter 11
PAD Message Set

Packet Format for PAD Mode

Using PAD Mode PAD Messages

11 6
corresponding reply packets. The STS value is either 00 to indicate a
successful transaction completion or a non-zero value to indicate an error.
If you initiate a series of PAD command packets without waiting for each
reply, there is no guarantee that the command packets will be delivered at
the destination in the same order in which you sent them. To guarantee
order of delivery, wait for each reply before sending the next command
packet.
A host computer for a 1779-KFM interface can send PAD messages to
and receive PAD messages from a host device for a 1779-KFL or
1779-KFM interface at another Data Highway II station. The host device
at the other station could be a dumb terminal, a robot, or a computer.
Figure 11.2 shows a PAD-mode data frame containing a PAD packet. The
PAD packet can contain a maximum of 256 bytes of application data in
any format. However, if the destination-station interface is in the Native
mode, the PAD packet must be limited to a maximum of
238 bytes.
Figure 11.2
PAD Format in PAD Mode
Application Fields
HDLC Data Link Fields
FLG ADDR
The format of all PAD-mode PAD messages is exactly as shown in
Figure 11.2. There is no provision for replies to confirm delivery of
messages to their destinations.
The PAD-mode format has no provision for specifying the destination
station for PAD messages. The destination station must be established
beforehand through station-management commands.
DATA (Any Format)
256 Bytes Max.
CTL DATA
(From Preceding Layer)
FCS FLG