User`s guide

transmitting a message.
If the ALERT ACK is not received in time, the SLTA-10
Adapter repeats the process by transmitting another ALERT byte.
The SLTA-10 Adapter cannot support a full duplex communications process between
it and the host. The network driver included with the SLTA-10 Adapter takes this
into account. Data frames transmitted to the SLTA-10 Adapter while it is in the
process of sending uplink messages will be lost if more than 16 bytes are sent to the
SLTA-10 Adapter.
Buffered Link Protocol
The DOS network driver uses the buffered link protocol when the /N option is
specified. See Chapter 8 for a description of this option. The UNIX network driver
uses the buffered link protocol if the alert-ack-prtcl variable is set to FALSE in
the source code (this is the default). The Switchl/CFG3 input of the SLTA-10
Adapter, as described in Chapter 4, must be in the buffered protocol state (VP
position).
When using this protocol, the link-layer header contains a length byte followed by a
one’s complement of the length byte.
These values are always validated by the
receiver before accepting the rest of the message.
Following the length bytes is the
network interface command.
See Appendix D of the Host Application Programmer’s
Guide for a description of the command byte structure.
If the message contains a
data field it follows the command byte. Finally, a checksum terminates the sequence.
Sender
Receiver
Link-Layer
Header
1 checksum [
Figure 9.3 SLTA-10 Adapter Buffered Link Protocol
The length byte value describes the length of the network interface command byte
plus the length of the data field. This value will always be at least 1. The checksum
is a two’s complement of the sum of the command byte and all of the bytes in the data
field, if it exists. Checksum errors detected by the host will cause an error to be
SLTA-10 Adapter User’s Guide
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