User guide

9: Client Applications — Commands and Responses
DC 900-1338I 183
At the ICP, the fields of the ICP and protocol headers that the ICP receives contain the
following values:
ICP_HDR
count = size of protocol header (16 bytes) plus size of data
command = DLI_ICP_CMD_WRITE
status = high bits indicate byte ordering
PROT_HDR
command = DLI_PROT_SEND_NORM_DATA
session = session ID
DATA AREA = data to be transmitted
The ICP protocol task prepares the data for transmission. If the protocol is bsc, the con-
figured number of sync characters are placed at the beginning of the message. If the pro-
tocol is async or bsc, the configured start character is placed immediately before the
client’s data. If the protocol is async, the configured stop character is appended. If a
CRC is configured, a CRC is calculated and appended. The ICP then activates the trans-
mit device for the protocol being used by that link.
When the message has been transmitted by the ICP, the client’s expected response is a
DLI_PROT_RESP_LOCAL_ACK message, as shown in Figure 9–19. The iICPStatus and
iProtModifier fields are zero, and there is no data area.
If the ICP cannot transmit the data, the client’s expected response is a
DLI_PROT_RESP_LOCAL_ACK message with iICPStatus and iProtModifier fields that
contain an error code. In this case, the data area contains the original data not sent.
Note
However, if the link was configured for a protocol without
Ack (see Figure9–12 on page 175), then there is no
DLI_PROT_RESP_LOCAL_ACK.