User`s guide

network driver. The read/write interface is implemented in the ldv-read ( ) and
ldv-wr i te ( ) functions for the UNIX network driver
The following files are unique to a DOS driver and would probably not be used in a
porttoanotherhost: MSD-DRVR.H,MSD-DIFC.C,MSD-FRST.~,MSD-LAST.C,
MSD-SEGD.ASM.
Network Interface Protocol
The network driver implements the host side of the network interface protocol,
providing an easy-to-use and interface-independent read/write interface to the host
application. The network interface protocol is a layered protocol that includes the
following layers:
l Presentation Layer. Defines packet formats for network variables and explicit
messages. This is the only layer visible to the host application. The remaining
layers are managed by the network driver.
l Session Layer. Manages flow control, buffer requests, and grants.
l Transport Layer. Ensures end-to-end reliability between the host and the
SLTA-10 Adapter.
l Link Layer. Controls access to the serial link.
l Physical Layer. EIA-232 interface.
The physical layer is defined by the EIA RS-232 standard. The link, transport,
session, and presentation layers are described in the following sections.
Link Layer Protocol
The default interface link layer protocol is the ALERTIACKprotocoZ.
This protocol
may be used when the host is a microcontroller or microprocessor such as a PC
running DOS or Windows. The alternative interface link protocol is the buffered
protocol. This protocol is used with computer hosts that can asynchronously buffer
an entire packet. All data are transmitted using 1 start bit, 8 data bits, no parity
bits, and 1 stop bit.
ALERT/ACK Link Protocol
The DOS network driver uses the ALERTlACK link protocol by default (i.e. the /N
option is not specified). See Chapter 8 for a description of the network driver
options. The UNIX network driver uses the ALERT/ACK link protocol if the
alert-ack-prtcl variable is set to TRUE in the source code (this is not the default).
The Switchl/CFG3 input of the SLTA-10 Adapter, as described in Chapter 4, must be
in the ALERTIACK state (DOWN position).
When using this protocol, all transfers between the SLTA-10 Adapter and the host
consist of serial data streams that start off with the link-layer header sequence
described in figure 9.2. Whenever one device, either the SLTA-10 Adapter or the host,
needs to send a command or message, the sender starts the sequence by transmitting
the ALERT byte (value 01 hex). When this byte is received by the receiver, that
SLTA-10 Adapter User’s Guide
9-5