User`s guide

78 DC 900-1340I
BSC Programmer’s Guide
3.4.3 Data Transfer using Raw dlWrite
The BSC 3270 software provides two write types (EOM and non-EOM) for each data
transfer to allow the user to send or receive a single message that is larger than the con-
figured ICP message buffer size. Each type of data block consists of n bytes of data,
where n is a number from 0 to the maximum data size specified by the Set ICP Message
Buffer Size command (Section 3.4.1.3). Set the MSB of the
pOptArgs.usProtCircuitID
field to the control unit number for the data transfer, and set the LSB to the device unit
number.
When the client computer sends a data block to a control station, BSC 3270 issues a
select sequence on the line in order to transmit the data. If BSC 3270 is currently receiv-
ing data from the line, the data block waits in memory until the current operation is
complete before attempting a select.
When the client sends a data block to a tributary station, the data block waits in mem-
ory until the station is polled. At that time, BSC 3270 transmits the data on the line.
If the localAck DLI configuration parameter is set to “no” (see the Freeway Data Link
Interface Reference Guide), the client application must make a
dlRead request to receive
the data acknowledge response for each
dlWrite data transfer request (the dlRead
pOptArgs.usProtCommand
field is set to DLI_PROT_RESP_LOCAL_ACK by the DLI). One
DLI_PROT_RESP_LOCAL_ACK response (with the dlRead pOptArgs.iICPStatus field set to 1,
signifying that one block of data was sent) is sent to the client computer after each data
block has been successfully transmitted to the remote computer, and can be treated by
the client program as the remote acknowledgment. Data acknowledgments are also
used to report transmission errors (as a response to a
dlRead request as described in
Section 3.5.3). The client application can use the data acknowledge response to monitor
the success or failure of transmitted data messages, or for regulating the number of out-
bound messages that the BSC software has pending transmission at any one time.
If the DLI localAck configuration parameter is set to “yes” (which is the default), the
data acknowledge response is implied by a successful
dlWrite.