Reset Request (Reset) Packet; Reset Confirmation (Rc) Packet; Receive Ready (Rr) Packet; Receive Not Ready (Rnr) Packet - Texas Instruments 990 User Manual

Introduction
Reset Request (RESET) Packet.
This packet requests that communications be restarted between the
pr imary station and a speci fi ed secondary station af ter network
errors have occurred.
Reset Confirmation (RC) Packet.
This packet is sent to acknowledge the receipt of a RESET packet
and to confi rm that the reset procedures have been performed.
Rece i ve Read y (RR) Pac ket •
This packet is sent to indicate that the transmitting station is
ready to receive another data packet. This occurs after the
station window fills and acknowledges any received data packets.
Recei ve Not Ready (RNR) Packet.
This is sent to indicate that the transmitting station cannot
recei ve more messages. The RNR and RR packets are used in
conjunction to regulate the flow of data packets through the
network.
1. 4.2 • 4 Level 4 (U ser I nterf ace) •
Level 4 provides the user with an interface to the HOLC
communications system. A tas k may access the HOLC communications
system using a supervisor call, SVC >40. When a task performs a
read or write operation (that is, when it receives or transmits),
the associ ated message is p:tssed to or from a OXIO communications
buffer via this
svc.
After the operation has been attempted, the
SVC returns control to the task, along with a status code
indicating the successful (or unsuccessful) completion of the
operation. Operation codes 2 and 3 are used wi th the SVC to
request read and wri te operations , respectively (discussed
further in Section 4). Figure 1-8 shows the flow of information
at the user interface level, including the relationship of
acti vation services and the NIT to this level. These areas are
described in the following paragraphs.
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