Envoy Application Programming Manual

Software Concepts
Envoy Application Programming Manual—427159-001
2-17
Polling Operation
For a tributary station, the address list contains the poll addresses and select addresses to
which the station responds. The address list for tributary station B in Figure 2-4,
Multipoint Connection, on page 2-15 is shown in Example 2-6 as follows:
Polling Operation
The poll list of the supervisor station defines all stations in the multipoint network to be
polled. The default case specifies that all stations in the poll list are to be polled when
polling is initiated. Specific stations in the poll list can be disabled for polling (that is,
bypassed) when the address list is defined. This permits all stations in the network to be
defined initially, but certain stations are not actually polled until later. Stations in the poll
list for which polling is disabled can be enabled for polling by way of the
CHANGELIST procedure. The CHANGELIST procedure is also used to disable the
polling of individual stations after the poll list has been defined.
Note. The application process appends an ENQ to the poll and select addresses. Additionally,
if the sum of the address length + 1 (for the ENQ character) is odd, then the poll address must
be preceded by an ASCII SYN character to pad the poll address out to an even length.
Example 2-6. Address List for Tributary Stations B and C
STRING .saddrlist[0:11] :=
[ syn, “BPOL”, 0, ! poll address.
syn, “2SEL”, 0 ]; ! select address.
INT linename [0:11] := [“$BTRIB”,9*[“ ”]],
linefnum,
.addrlist := @saddrlist ’>’ 1;
CALL OPEN (linename, linefnum);
.
.
.
CALL DEFINELIST(linefnum,addrlist,3,2,1,0);
For tributary station C in Figure 2-14, the address list is as follows:
STRING .saddrlist[0:11] :=
[ syn, “CPOL”, 0, ! poll address.
syn, “3SEL”, 0 ]; ! select address.
INT linename [0:11] := [“$CTRIB”,9*[“ ”]],
linefnum,
.addrlist := @saddrlist ’>’ 1;
CALL OPEN (linename, linefnum);
.
.
.
CALL DEFINELIST(linefnum,addrlist,3,2,1,0);