SEMI E30-0299 ã
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ã SEMI 1992
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Equipment Terminal Services
Error Messages
Clock
Spooling
Control
4.1 Establish Communications — The Establish
Communications capability provides a means of
formally establishing communications following system
initialization or any loss of communications between
communicating partners, and thus of notifying the
communication partner that a period of non-
communication has occurred.
4.1.1 Purpose — Communications between host and
equipment are formally established through use of the
Establish Communications Request/Establish
Communications Acknowledge transaction.
The use of S1,F1/F2 for this purpose is ambiguous since
the transaction can be used for other purposes and may
occur at any time.
The S1,F13/F14 transaction, used in conjunction with
the Communications State Model, provides a means for
equipment to notify the host, or the host to notify the
equipment, that there has been a period of inability to
communicate. The successful completion of this
transaction also signals a possible need for
synchronization activities between host and equipment.
4.1.2 Definitions
COMMACK— Acknowledge code returned in the
Establish Communications Acknowledge message. See
the SEMI E5 Standard for a full definition of this data
item.
EstablishCommunicationsTimeout —Anequipment
constant used to initialize the interval between attempts
to re-send an Establish Communications Request. This
value specifies the number of seconds for the interval.
See the SEMI E5 Standard for a full definition of this
variable data item.
4.1.3 Description — There are potential problems
when one side of the communications link fails and the
other side does not detect it. From the point of view of
the host, a loss of communications has many possible
causes. In some cases, host-controlled settings on the
equipment may need to be reset. In other cases, the
equipment may have continued an automatic processing
sequence during the period of no communication and
may have changed states. The definition of a formal
protocol for establishing communications alerts the host
to the need to synchronize itself with the equipment's
current status.
Equipment shall consider communications as formally
established whenever either of the following conditions
have been satisfied
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:
— Communications Request has been sent to the host
and an Establish Communications Acknowledge
has been received within the transaction timeout
period and with an acknowledge code of Accept, or
— Communications Request has been received from
the host, and an Establish Communications
Acknowledge response has been successfully sent
with an acknowledge code of Accept.
When the equipment sends an Establish
Communications Request to the host, this notifies the
host of the possible need to synchronize itself with the
equipment.
When the equipment is attempting to establish
communications, an Establish Communications Request
shall be sent periodically until communications have
been formally established as described above. The
interval between attempts must be user-configurable and
begins as soon as a connection transaction failure is
detected (see Section 3.2).
Attempting to establish communications is not a low-
level connectivity issue, but rather a logical application
issue used by either party to notify its partner that the
host may need to perform synchronization activities
with the equipment.
4.1.4 Requirements
— Equipment must support the Communication State
Model (see Section 3.2).
— Equipment must provide the EstablishCommunica-
tionsTimeout equipment constant described above.
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Satisfaction of either of these conditions will result in a transition
to the COMMUNICATING substrate. See Section 3.2 for further
detail.