3.6.2 The physical devices
There are many possible physical devices which can be attached to a computer.
Examples
of
such devices are printers, plotters, modems, and video monitors.
They all have one thing in common, they involve the transfer
of
information
to
or from the computer. The physical devices are given symbols in
CP
1M
which
like the logical symbols relate
to
their function. A computer manufacturer may
not
support each device, and different manufacturers may give different as-
signments to the same device. The symbols corresponding to the physical devices
are:
TTY: denotes a slow speed terminal. Its name
is
derived from the
TeleTYpewriter, which has a keyboard
and
printer as input and output devices
for the user
to
communicate with the computer.
CRT: represents a high speed console device. Its name
is
derived from the
commonest type
of
device a Cathode Ray Tube.
BAT: denotes a BATch processing device, which historically relates to devices
such as punched card readers.
UCI:
denotes a User defined Console device, which allows special console
equipment
to
be used.
PTR:
corresponds
to
a Paper Tape Reader.
.
URI:
and UR2: correspond to two different User defined Reader devices. They
enable a computer manufacturer
to
provide two different high speed devices
for input
of
data.
PTP:
denotes a Paper Tape Punch device for output
of
data
to paper-punch
equipment.
UPI:
and UP2: correspond to two different User defined Punch devices. They
enable a computer manufacturer to output data
to
two high speed output devices.
LPT:
is
a Line PrinTer which allows data
to
be printed for a permanent record.
ULI:
is
a User defined List device.
It
enables the computer manufacturer to
provide
an
interface for communication
to
special devices such as plotters.
3-14
3.6.3 Physical Devices Supported by the PX-8
The PX-8 does not have all the physical devices which could be supported by
CP
1M.
The physical devices which the PX-8 has are:
1)
The LCD display.
2)
The keyboard
3)
High speed serial port, which
is
used to communicate with floppy disk drives,
printers and other special devices.
4)
RS-232 serial port, which
is
used to communicate with other computers and
also printers.
A computer manufacturer has
to
modify
CP
1M
so
that
a particular physical
device corresponds
to
one
or
more
of
the names allowed by
CP/M.
A device
can correspond to more than one name, and each
of
the logical devices can
be connected to more
than
one physical device. The four logical devices can
be assigned
to
the physical devices as follows:
Table 3.1
Logical Device
1/0
Physical Device
LST:
TTY: CRT: LPT:
ULI
0
Serial (printer) LCD display
RS-232C not implemented
PUN: TTY:
PTP
UPI:
UP2:
0
not implemented LCD display RS-232C
not implemented
RDR: TTY: PTR:
URI:
UR2:
I keyboard not implemented RS-232C
not implemented
CON: TTY CRT: BAT:
UCI:
output
0 RS-232C LCD RS-232C
RS-232C
input
I keyboard keyboard
RS-232C RS-232C
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