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CHAPTER VII
I/O DRIVERS AND COMMANDS
The term "I/O Driver" refers to a routine used to transfer
textual data between the ALS-8 routines (or user routines) and
an associated input or output device. Its basic duties are to
interpret a request for data transfer from some calling routine
and to translate it into a sequence of reads or writes suited to
the conventions assumed by the electronics of the external
device. This relieves the calling routine of the responsibility
of handling separate conventions for many devices.
Conceptually, an ALS-8 routine can ask for data from any input
device in the same way or send data to any output device. It
must formulate the request and simply choose the routine to
handle the request and the device.
The ALS-8 has a table of driver routines in its system RAM
area and a parameter identifying the current pair of drivers
(input and output). When an ALS-8 function requires input or
output of a character, it uses this parameter to choose the
proper driver. The table for these routines contains a name and
pair of addresses for each entry. The IODR command handles
entries to and deletions from this table, as well as defining
the "current" driver and printing out the table's contents.
Used with a name argument of one to five characters and two
numeric arguments obeying the current value of MODE, the IODR
command will enter the name and addresses into the table. If
used with no arguments at all, IODR prints the contents of the
table. Since drivers are selected as pairs, special functions
can be implemented such as read from high speed paper tape both
with and without printout. Entries can be deleted by using IODR
with the entry name as an argument followed by a single zero
argument. The example shows IODR being used in these ways.
IODR /TAPES/
DF00
DF40
TAPES DF00 DF40
IODR /TVTWT/
DF80
DFC0
TVTWT DF80 DFC0
IODR
SYSIO E200
TAPES DF00
TVTWT DF80
E240
DF40
DFC0
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