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SEMI E30-1103 © SEMI 1992, 2003 26 Thus, UPPERDB and LOWERDB as a pair define a limit. LOWERDB — A variable limit attribute that defines th e lower boundary of the deadband of a lim it. 18 The value applies to a single l…

SEMI E30-1103 © SEMI 1992, 2003

4.2.3.5 Scenario

Host Initiates Trace Report:

COMMENT HOST EQUIPMENT COMMENT

Trace Data initialization

requested S2,F23-->

<--S2,F24 Acknowledge, trace initiated

[DO] TOTSMP REPGSZ times

[DO] REPGSZ many times: collect

SVID

,...SVID

data, delay

time by DSPER.

[END_DO]

<--S6,F1 Send SV

,...SV

Acknowledge receipt S6,F2-->

[END_DO]

Optional:

Request trace termination prior to

completion (TOTSMP = 0) S2,F23-->

<--S2,F24 Acknowledge premature termination

4.2.4 Limits Monitoring — This capability relates to the

monitoring of selected equipment variables and has

three primary aspects:

— Defines a standard set of monitoring zones and

limits.

— Provides for reporting to the host when selected

equipment variables transition between monitoring

zones.

— Empowers the host to modify the values of the

variable limit attributes for these same selected

equipment variables.

4.2.4.1 Purpose — The limits monitoring capability

provides the host a means of monitoring equipment

conditions by a flexible, efficient, and asynchronous

method which is consistent across equipment. It

eliminates the need for constant polling of equipment

by the host for current status values. Further, this

capability allows the host to implement changes in the

monitoring range as needed. This capability has

application to both production operation and

diagnostic/testing scenarios, and it also has applicability

to statistical process control.

4.2.4.2 Definitions

LimitVariable — DVVAL containing the VID of a

specific equipment variable for which a zone transition

collection event has been generated.

EventLimit — DVVAL containing the LIMITID of the

limit crossed by LimitVariable.

TransitionType — DVVAL which defines the direction

of the zone transition which has occurred: 0 = transition

from lower to upper zone, 1 = transition from upper to

lower zone.

Limit — Used in this section to represent the set of

variable limit attributes that completely describe a

variable monitoring “barrier.” The attributes include

VID, Units, UPPERDB, LOWERDB, LIMITMAX, and

LIMITMIN. In some contexts it may be interpreted

more narrowly as the combination of UPPERDB and

LOWERDB.

LIMITID

— Refers to the identifier of a specific limit

(as defined by UPPERDB and LOWERDB) among the

set of limits for a monitored equipment variable.

LIMITIDs are consecutively numbered, beginning at

one through the number of limits possible (seven

minimum).

Monitoring Zone — A subset of the possible range of

values for a variable of interest to the host. A single

limit divides the range into two zones. Multiple limits

may be combined to divide the range even further.

Zone Transition — The movement of a variable value

from one monitoring zone to another. This transition is

a collection event and has a corresponding CEID.

Deadband — An overlap of two zones implemented to

prevent constant zone transitions by a variable sitting

on or near a limit (i.e., “chattering”).

UPPERDB — A variable limit attribute that defines the

upper boundary of the deadband of a limit.

The value

applies to a single limit (LIMITID) for a specified VID.

18 The format and units must be the same as the format of the

variable being monitored.

SEMI E30-1103 © SEMI 1992, 2003

Thus, UPPERDB and LOWERDB as a pair define a

limit.

LOWERDB — A variable limit attribute that defines the

lower boundary of the deadband of a limit.

The value

applies to a single limit (LIMITID) for a specified VID.

Thus, UPPERDB and LOWERDB as a pair define a

limit.

UPPER ZONE — The range of values lying above a

limit.

LOWERZONE — The range of values lying below a

limit.

LIMITMAX — The maximum value for any limits of a

specific equipment variable. This value is set by the

equipment manufacturer and typically coincides with

the maximum value allowed for the monitored variable.

LIMITMIN — The minimum value for any limits of a

specific equipment variable.

This value is set by the

equipment manufacturer and typically coincides with

the minimum value allowed for the monitored variable.

Undefined — When used in reference to variable limits,

it indicates that monitoring/reporting of zone transitions

involving that particular limit are disabled.

4.2.4.3 Description — The limits monitoring capability

provides the host with a minimum of seven

configurable limits or barriers that may be applied to

selected equipment status variables (SV’s) of the types

floating point, integer, and boolean. When one of these

barriers is crossed, a collection event is generated to

alert the host to a change in monitoring zone or state of

the monitored variable. These seven limits may be

combined in a variety of ways to match the needs of the

host system.

An illustration of a combination of five

of the limits to provide one type of variable monitoring

is shown in Figure 4.2.1.

This section describes the

key aspects of limits monitoring. Detailed

implementation examples of limits monitoring are

provided as Application Note A.7.

NOTE 6: While the SEMI E5 standard allows SV’s to be lists,

such variable lists are not allowed under this capability.

4.2.4.3.1 Monitoring Limit Characteristics — A limit

is defined by a set of attributes that include the variable

(VID) to which the limit corresponds, the units of that

variable, the maximum and minimum possible values of

19 Note that while at least seven limits per variable are available from

the equipment, the host need not use all seven.

20 This illustration shows the reading which might be available to the

equipment, not the limit excursions reported to the host. Reporting is

covered later in the section.

the limit (LIMITMAX and LIMITMIN) and the

specific borders of the limit (UPPERDB and

LOWERDB). See Figure 4.2.2. There is a limitation to

the values of UPPERDB and LOWERDB which may

be stated as:

LIMITMAX≥UPPERDB≥LOWERDB≥LIMITMIN

A limit divides the possible range of variable values

into two parts, the upper zone and the lower zone. At

any time, the monitored variable is considered to be in

one and only one of these zones. However, as Figure

4.2.2 shows, these two zones have an area of overlap.

This is called the deadband.

Figure 4.2.1

Limit Combination Illustration: Control

Application

Figure 4.2.2

Elements of One Limit

The deadband is a key concept of limits monitoring,

especially for floating point variables. Its purpose is to

prevent a phenomenon known as chattering — the

repeated changing of zones due to small, rapid

fluctuations in variable value while near the zone

boundary. In practice, the value of a variable must

reach the opposite boundary of the deadband before a

zone transition can occur. Thus, if a variable’s value

SEMI E30-1103 © SEMI 1992, 2003

reaches the UPPERDB and transitions into the upper

zone, it will not return to the lower zone until it falls

back to the LOWERDB. The difference between

UPPERDB and LOWERDB should always be greater

than the typical amplitude of those fluctuations deemed

to be insignificant. In some cases, the width of the

deadband may set to zero (i.e., UPPERDB =

LOWERDB). At first glance, this would seem to make

indeterminate the current zone when an integer value

sits on the limit. This is not the case, however, when

movement of the value is considered. To illustrate, an

example is given, assuming that UPPERDB =

LOWERDB = 100. The list shows consecutive readings

of the variable and the resultant zone:

99 Lower Zone (Initial Reading)

101 Upper Zone (Zone Transition)

100 Lower Zone (Zone Transition)

100 Lower Zone

99 Lower Zone

100 Upper Zone (Zone Transition)

Transition from one zone into another generates a

collection event, as might be reported via S6,F11. The

host has the option of receiving notification by enabling

event reporting for the event. For each variable that has

monitoring capability, one CEID is reserved to indicate

zone transitions for that variable. To aid in the

determination of the nature of a transition event, three

DVVAL’s have been defined:

LimitVariable — The VID of the monitored variable to

which the collection event refers.

EventLimit — Contains the LIMITID of the limit

reached or crossed by LimitVariable.

TransitionType — Defines the direction of the zone

transition which has occurred: 0 = transition from lower

to upper zone, 1 = transition from upper to lower zone.

Sampling frequency is an important element of limits

monitoring and should be considered during equipment

specification. If changes in variable value are relatively

fast compared to sampling frequency, it is possible for

some zone transitions to be missed or for multiple zone

transitions to occur between readings. Since it is

possible for zone transitions to occur “simultaneously”

or for limits to be identically defined, the DVVAL

EventLimit has been defined to allow for a list of

multiple zone transitions of a variable to be reported

with a single collection event.

It also should be emphasized that a single CEID is used

to report transitions in both directions across a limit.

Thus, reporting for one direction but not the other

cannot be configured.

The functionality of each limit for each variable can be

described with the state model shown in Figure 4.2.3.

Below, the three states are described more fully,

followed by a table defining the transitions.

Figure 4.2.3

Limit State Model

ABOVE LIMIT

A variable is considered to be above a limit when its

value increases to equal or exceed the upper boundary

of the deadband, UPPERDB. The significance attached

to this state is a function of the host’s usage.

BELOW LIMIT

A variable is considered to be below a limit when its

value decreases to equal or fall below the lower

boundary of the deadband, LOWERDB. The

significance attached to this state is a function of the

host’s usage.

NO ZONE

In some circumstances it is possible for the variable

value to be in neither the upper zone nor the lower

zone. This may occur upon definition of a new limit or

upon equipment startup when the value of the variable

lies in the deadband. In this case, the active state of the

limit is considered to be NO ZONE. The limit shall

remain in this state until the variable value reaches

either boundary of the deadband.