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Browse Prior Art Database

BIOS Function Calls for a Display Adapter Serial Link

IP.com Disclosure Number: IPCOM000111805D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 211K

Publishing Venue

IBM

Related People

Blackledge, J: AUTHOR [+3]

Abstract

Described is a set of function calls for use as an extension to BIOS code to provide a software link to a Display Adapter Serial Link (DASL), which in turn provides a means for connecting to, and communicating with, a number of different devices attached to the serial link. These function calls provide a BIOS layer increasing the usability of the DASL communications link, which is a device-independent communications protocol allowing devices within a system unit to communicate with the display unit and with other devices connected to the display unit. A number of different types of devices may be connected concurrently in this way. With this BIOS layer, it is not necessary to replicate the DASL software for each using device.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 26% of the total text.

BIOS Function Calls for a Display Adapter Serial Link

      Described is a set of function calls for use as an extension to
BIOS code to provide a software link to a Display Adapter Serial Link
(DASL), which in turn provides a means for connecting to, and
communicating with, a number of different devices attached to the
serial link.  These function calls provide a BIOS layer increasing
the usability of the DASL communications link, which is a
device-independent communications protocol allowing devices within a
system unit to communicate with the display unit and with other
devices connected to the display unit.  A number of different types
of devices may be connected concurrently in this way.  With this BIOS
layer, it is not necessary to replicate the DASL software for each
using device.

      With this layer, BIOS provides a software interrupt (INT) base
interface to common code, with a set of commands linked to an
appropriate interrupt vector number, herein indicated as INT NN.  The
DASL BIOS layer provides an application with the Link Layer and
Physical Layer protocols.  Application dependencies are removed from
the DASL link in the Link Layer.  The DASL link layer transports data
it receives from the application layer to the remote end of the link,
ensuring the delivery of data without intervention by the application
itself.  To achieve this, messages are acknowledged with link message
timers, reacting to no-response conditions.  If the checksum feature
is enabled, the physical layer computes the checksum, informing the
DASL link layer if an error is indicated.

      Before transfer commands, the application must ensure that the
link is initialized.  Once the link is initialized, various commands
can be issued, initiated by (AH) = 01 to 0D, along with the interrupt
INT NN.  Upon completion of each of the following commands, (BL)
contains the status of the station, with Bits 6 and 7 being reserved,
Bit 5 indicating an interrupt, Bit 4 indicating a bus request, Bit 3
indicating request complete, Bit 2 indicating the bus is busy, Bit 1
indicating the input buffer is full, and Bit 0 indicating the output
buffer is full.  Wherever a port base address is required, if a value
of 00 is specified, a default address is used.

      The SEND A BYTE ON THE LINK command is initiated, with (AH) =
01, to transmit a single byte of data on the DASL link, which must be
activated, with the transmit buffer empty, before this command is
invoked.  The application must send bytes in a particular order.  The
code can be returned after the byte is transferred or immediately.
The parameters sent to BIOS are (AL) = the byte of data to be sent,
(DX) = the port base address, and (BH) = attributes.  Either an
address or a handle can be provided.  In (BH), Bit 7 indicates that
the wait for transmission is complete, Bit 6 indicates that this is
the last byte to be transmitted, and Bit 5 activates a transmit time
out.  The parameters re...