User`s guide

66 DC 900-1340I
BSC Programmer’s Guide
Safe Store on BSC 3270 Tributary Stations
Unlike the control station, a tributary station is unable to send WACKs on the line to
keep it active. In the 3270 protocol, a WACK from a tributary station constitutes a pos-
itive acknowledgment thus barring its use for safe store operation. Instead of sending
WACK, a tributary station sends no response until it receives a Safe Store Acknowledge
command (or Send EOT command) from the client even after it receives an EOT from
the control station.
3.4.1.9 BSC 3270 Specific Poll Command
Use the dlWrite function with the pOptArgs.usProtCommand field set to
DLI_PROT_SET_SPECIAL_POLL to issue a specific poll to a device. Set the MSB of the
pOptArgs.usProtCircuitID field to the control unit number and set the LSB to the device
unit number. The format of the Specific Poll is shown in Figure 3–4. CUA represents the
control unit address and DA the device address, which the BSC software derives from
the CU and DU numbers specified by the client application.
The dlRead response to this command is either a data message from the control unit and
device specified, or a station up or down error report.
An unsuccessful Specific Poll command can return the following error code in the
dlRead pOptArgs.iICPStatus field (see Appendix D for error handling):
DLI_ICP_ERR_BAD_MODE
The function request is not available for the requested
access mode.
Figure 3–4: BSC 3270 Specific Poll Format
SYN SYN EOT SYN SYN CUA DA DA ENQ PADCUA