User`s guide

34 DC 900-1340I
BSC Programmer’s Guide
2.1.1 3270 Control Station Operation
A link configured as a control station can poll up to 32 tributary stations (control units).
Tributaries may be added to or removed from the polling list at any stage of link oper-
ation. Data blocks received from tributary stations are marked with the sender’s control
unit (CU) number and device unit (DU) number. The control station selects tributary
stations when it has data to send. The client application program provides the CU and
DU numbers for outbound data blocks.
2.1.2 3270 Tributary Station Operation
A link configured as a tributary station operates much like a single IBM 3274 control
unit with the client application program acting as one or more (up to 32) attached
devices. The client application program uses the station ID option (Section 4.16 on
page 97) to specify the control unit number before link startup. The tributary station
responds to all poll or select sequences that match its CU number and ignores all other
input.
A link may also be configured in tributary “test mode” by setting the station ID option
to 32. In test mode, a single link can appear to a master control station as multiple con-
trol units. Control unit numbers for each control unit to be active are placed in the poll
list (Section 3.4.1.7 on page 62).
2.1.3 Transmission Codes
The Protogate BSC software can transmit and receive data in either the American Stan-
dard Code for Information Interchange (ASCII) character set or the Extended Binary
Coded Decimal Interchange Code (EBCDIC) character set depending on the setting of
the BSC character set option (Section 4.7 on page 91). The data transferred between the
client program and the BSC software is always in ASCII and is translated by the BSC
software as required.