Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

Chapter 2 43
Controlling Asynchronous Devices Programmatically
File System Overview
be suited to the characteristics being specified. Data directed to
terminals or printers, for example, must be in ASCII format, and have a
blocking factor of 1. These are device-dependent characteristics, and
if you try to specify something different it will be overridden. See the
Accessing Files manual for a summary of device-dependent
characteristics.
File System Hierarchy
There is a basic hierarchy to the way the File System overrides file
specifications. Device dependence is at the top of the hierarchy and will
override any attempts to modify file characteristics in a manner
inappropriate to the device being used. Figure 2-1 shows which
methods of specifying file characteristics take precedence in the File
System hierarchy.
Figure 2-1 File System Hierarchy
The FFILEINFO intrinsic can be used to determine what specifications
are currently in place for a given file. FFILEINFO is described in more
detail in Chapter 8, “Intrinsics Reference,” of this manual.
See the Accessing Files manual for detailed information on the MPE/iX
File System.
DEVICE DEPENDENT CHARACTERISTICS
FILE EQUATION SPECIFICATION
HPFOPEN/FOPEN SPECIFICATION
FILE SYSTEM DEFAULTS
overrides
overrides
overrides