Basic
I/O
System (BIOS) Functions
5-6
Simple
Character
1/0
Subroutines
This section describes how simple character
inputloutput
operations are performed
with
CP/M-86
using BIOS functions 2
through
7.
It
also describes the operation
of
the IOBYTE
and
the functions
(9
and
20)
that
set
and
read this field.
SIMPLE
PERIPHERAL
DEVICES
All simple character
1/0
operations are assumed to be performed in ASCII, upper
and
lower case, with high
order
(parity) bit set
to
zero.
An
end-of-file condition for
an
input
device
is
given by
an
ASCII
CONTROL-Z
(lAH).
Peripheral devices are
seen by
CP/M-86
as "logical" devices,
and
are assigned to physical devices within
the
BIOS. Device characteristics are defined in Table 5-2.
Table
5-2
CP
IM-86 Logical Device Characteristics
DEVICE
NAME
CHARACTERISTICS
CONSOLE
The principal interactive console which communicates with
the operator, accessed through
CONST,
CONIN,
and
CONOUT. Typically, the CONSOLE
is
a device such as a
CRT
with a keyboard,
or
Teletype.
LIST
The principal listing device,
ifit
exists
on
the system, which
is
usually a hard-copy device such as a printer
or
Teletype.
PUNCH
The principal tape punching device,
if
it exists. Any RS 232C
device, such as a modem, can also be used.
READER
The principal tape reading device, such as a simple optical
reader
or
Teletype. Any RS 232C device, such as a modem,
can also be used.
Note
that
a single peripheral can be assigned as the LIST,
PUNCH,
and
READER
device simultaneously.
If
no peripheral device
is
assigned as the LIST,
PUNCH,
or
READER
device, the CBIOS gives
an
appropriate error message so
that
the system
does
not
"hang" if the device
is
accessed by PIP
or
some other transient program.
Alternately, the
PUNCH
and
LIST subroutines can simply return, and the
READER
subroutine can return with a
lAH
(CONTROL-Z) in register
AL
to
indicate immediate end-of-file.
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