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SEMI E30-1103 © SEMI 1992, 2003 28 4.2.4.3.2 Modification of Limit Values — Values for the monitoring limits on any monitored variab le may b e modified by the host using the m essage transaction S2,F45/F46 (Define Varia…

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.

SEMI E30-1103 © SEMI 1992, 2003

4.2.4.3.2 Modification of Limit Values — Values for

the monitoring limits on any monitored variable may be

modified by the host using the message transaction

S2,F45/F46 (Define Variable Limit Attributes). The

equipment must reject any S2,F45 message which

contains limit information which conflicts with the

following rules:

— LIMITMAX≥UPPERDB≥LOWERDB≥LIMIT-

MIN;

— If either UPPERDB or LOWERDB is defined,

both must be defined; if either UPPERDB or

LOWERDB is undefined, both must be undefined.

The first rule is defined and graphically depicted in

Figure 4.2.2. The second rule refers to the host’s ability

to turn any limit “on” or “off”. While a minimum of

seven limits must be available for each monitored

variable, it will be common for the host application to

require less than seven or even none of the limits be

used. The limits not needed can be disabled by leaving

the values for UPPERDB and LOWERDB

“undefined”. Limits may be disabled for a VID or for

all monitored VIDs by using zero length lists in the

S2,F45 message.

All monitored variables must be one of three types:

integer, floating point, or Boolean. This may be

accomplished by using the following formats: 11, 20,

3(), 4(), 5().

NOTE 7: The binary format is not allowed. If the ASCII

format is used, the equipment shall perform a conversion into

one of the numeric types before performing any value

comparisons, both for limit validations and zone transitions.

4.2.4.3.3 Limit Values Request — The host may

request the current limit values for a specified VID

using the message transaction S2,F47/F48 (Variable

Limit Attribute Request).

4.2.4.4 Requirements

— A minimum of seven limits per monitored variable

must be available.

— One CEID per monitored variable must be supplied

for zone transition reporting.

— All limit definitions must be kept in non-volatile

storage.

— The equipment must enforce the limit validation

rules defined above.

— The specification and documentation of which

variables may be monitored with this capability is

the responsibility of the equipment manufacturer

based on the specific instance of equipment. This

subject also may be addressed by equipment models

of classes of semiconductor equipment.

Table 4.2 Limit State Transition Table

# Current State Trigger New State Action Comment

1 DISABLED Limit attributed defined w/

S2,F45.

ENABLED None The substate of ENABLED is

determined by the current value of

the monitored variable.

2 ENABLED Limit attributes set to

undefined w/ S2,F45.

DISABLED None None

3 BELOW LIMIT Variable Increased to be

≥UPPERDB

ABOVE LIMIT None Zone Transition.

4 ABOVE LIMIT Variable decreases to be

≤LOWERDB

BELOW LIMIT None Zone Transition.

5 NO ZONE Variable decreases to be

≤LOWERDB

BELOW LIMIT None Zone Transition.

6 NO ZONE Variable increases to be

≥UPPERDB

ABOVE LIMIT None Zone Transition.

4.2.4.5 Scenarios — Zone Transition Event occurs in equipment:

COMMENTS HOST EQUIPMENT COMMENTS

Send enabled event report to host as shown in Section 4.2.1.

Host defines Limit Attributes:

COMMENTS HOST EQUIPMENT COMMENTS

[IF] S2,F45 is Multi-block

[THEN] Send Multi-block inquire S2,F39-->

<--S2,F40 Multi-block grant.

[END IF]

Host defines new variable limit

attributes. S2,F45-->

<--S2,F46 Equipment acknowledges host

request.

Host queries equipment for current Limits:

COMMENTS HOST EQUIPMENT COMMENTS

Host queries equipment S2,F47-->

for current variable limit

attribute definitions.

<--S2,F48 Equipment returns report

containing requested variable

limit attribute values.

4.2.5 Status Data Collection

4.2.5.1 Purpose — This capability allows the host to query the equipment for selected status information and is

useful in synchronizing with equipment status.

4.2.5.2 Definitions

Status variable value (SV) — A data item containing the value of a status variable. See SEMI E5 for a full definition

of this data item.

Status variable ID (SVID) — A unique identifier of a status variable. See SEMI E5 for a full definition of this data

item.

4.2.5.3 Detailed Description — The host may query equipment status by specifying the desired SVID’s. Upon such

a request, the equipment sends the host the value of the selected status variables. The host also may request the

description (name and units) of any or all available status variables.

4.2.5.4 Requirements

— The equipment manufacturer must provide unique SVID’s for the various status variables (SV) available for data

collection in the equipment.

— All status data is available for status data collection. See Section 5.2, Variable Item List, for a list of status

variables.

— All SV’s must contain valid data whenever provided to the host.