User`s guide

58 DC 900-1516D
ICP2432 User’s Guide for OpenVMS Alpha (DLITE Interface)
4.1.1 Channel Assignment
The VMS application program must assign a channel to the device driver before any I/O
can take place. To do this, the program uses the
SYS$ASSIGN system service. The
format of this system service is shown in Section 4.2.1 on page 61. Once a VMS pro-
gram assigns a channel to an ICP, it has access to all communication ports on that ICP.
A program can access more than one ICP by assigning a separate channel for each
board. Multiple VMS programs can access the same ICP board by assigning channels to
the same device name. Read and write operations for each of the programs are kept sep-
arate through the use of node numbers (described in Section 4.3.2 on page 75).
4.1.2 $QIO Interface
On VMS systems, application programs communicate with the ICP protocol software
through the use of the $QIO system service. The format of the
SYS$QIO call as it relates
to the ICP device is shown in Section 4.2.4 on page 63. More detailed information on
the QIO call and parameters can be found in the VMS System Services Reference Manual.
The following sections describe parameters that have specific use with ICP protocol
applications.
4.1.2.1 I/O Function Code
The I/O function code determines whether the QIO operation is a read or a write. Use
IO$WRITEVBLK (write virtual block) when writing a buffer to the ICP and IO$READ-
VBLK
(read virtual block) when reading a buffer from the ICP. No other modifiers are
required. The function codes for logical block (
IO$WRITELBLK, IO$READLBLK) and
physical block (
IO$WRITEPBLK, IO$READPBLK) are also supported, but are normally
not used by ICP programmers.