Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols

EnvoyACP/XF Application Programming Manual–132179

3-21

Nonresponding Station List

EnvoyACP/XF maintains a nonresponding station list to track the stations that do not

respond to polling. If a polled station does not respond with data or a supervisory frame

within the configured timeout period, EnvoyACP/XF puts the station address on the

nonresponding station list. EnvoyACP/XF considers stations on the list to be in an

error-stop state and does not poll them during subsequent polling cycles.

A multipoint supervisor or tributary station reenables tributary stations that are in the

nonresponding list in one of the following ways:

•

Defines a new address list by using the DEFINELIST procedure

•

Clears the nonresponding list by using the CHANGELIST procedure

A supervisor can use CHANGELIST to temporarily remove one or more stations from

the nonresponding station list.

A tributary uses CHANGELIST to manipulate its poll-bit state. The poll-bit state

determines whether a tributary station responds to a poll of the designated station

address.

By periodically clearing the nonresponding station list, the application process can

detect stations that are coming online. However, the application process should track

stations that do not respond within a specified number of polling cycles. Eventually, the

supervisor will set the poll state to disable polling of any permanently nonresponding

stations.

Station List Format

The station list in a multipoint supervisor specifies the station addresses of all tributary

stations in the network. The station list in a multipoint tributary specifies the station

address(es) to which that station responds. Both supervisor and tributary applications

use the DEFINELIST procedure to pass the station list to EnvoyACP/XF.

Each entry in the station list can be referred to by an entry number or index within the

range 0 through 255. The first station in the list is entry number 0, the second is number

1, and so forth. When the READ procedure completes, EnvoyACP/XF uses the entry

number to indicate to the application process which station address caused the

completion. For WRITE or WRITEREAD requests, the application process uses the

station index to designate the station selection for WRITE procedures. EnvoyACP/XF

and the application process pass the station index back and forth through bits 8 through

15 of the MCW.

Format of Station Address Lists

The station list requires four words fixed for each entry.

The following example shows how to build station address lists using basic 1-octet

addresses.

LITERAL addr^a = %40400, ! Station A address

addr^b = %41000, ! Station B address

addr^c = %41400, ! Station C address