SNAX/APN Application Programming Manual

The SNALU Interface
SNAX/APN Application Programming Manual—420111-001
4-5
Sending and Receiving BIUs: WRITEREAD
Procedure
For PLU processes on a Tandem system, this control bit is set to 1 in all incoming
CINIT and CTERM requests.
For SLU processes on a Tandem system, this control must be set to 1 in all outgoing
•
INIT-SELF requests
•
TERM-SELF requests
•
Character-coded logon requests
•
Character-coded logoff requests
This control is set to 1 in all incoming
•
INIT-SELF responses
•
TERM-SELF responses
•
LOGON responses
•
LOGOFF responses
Status Codes
SNAX/APN uses bytes 2 and 3 of the SNAX header for returning reason codes that
explain its failure to transmit an outbound BIU. The possible values for this field are
described in Appendix B of this manual.
Sequence Number
Bytes 4 and 5 of the SNAX header contain the sequence number associated with each
incoming or outgoing BIU. The application is responsible for setting, incrementing, and
checking the BIU sequence numbers.
Request/Response Header (RH)
SNA defines a 3-byte header that precedes each request/response unit (RU). This
header, referred to as the request/response header (RH), specifies bit-encoded control
information that pertains to the transmission of the associated BIU. For more
information about the request/response header, see the IBM manual Systems Network
Architecture: Network Product Formats or Systems Network Architecture: Format and
Protocol Reference: Architectural Logic.
Sending and Receiving BIUs: WRITEREAD
Procedure
SNALU applications use WRITEREAD procedure calls to send outgoing BIUs and to
receive incoming BIUs.
The general form of a WRITEREAD call is:
CALL WRITEREAD (filenum, buffer, write-count, read-count
[ , count-read ] )