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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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