Epson PX-8 User Manual page 47

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.
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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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