Calculation Record (calc)

The calculation or "Calc" record is used to perform algebraic, relational, and logical operations on values retrieved from other records. The result of its operations can then be accessed by another record so that it can then be used.

Parameter Fields

The record-specific fields are described below, grouped by functionality.

Scan Parameters

The Calc record has the standard fields for specifying under what circumstances the record will be processed. These fields are described in Scan Fields.

FieldSummaryTypeDCT DefaultReadWriteCA PP
SCANScan MechanismMENU (menuScan)Yes YesYesNo
PHASScan PhaseSHORTYes YesYesNo
EVNTEvent NameSTRING [40]Yes YesYesNo
PRIOScheduling PriorityMENU (menuPriority)Yes YesYesNo
PINIProcess at iocInitMENU (menuPini)Yes YesYesNo

Read Parameters

The read parameters for the Calc record consist of 12 input links INPA, INPB, ... INPL. The fields can be database links, channel access links, or constants. If they are links, they must specify another record's field or a channel access link. If they are constants, they will be initialized with the value they are configured with and can be changed via dbPuts. They cannot be hardware addresses.

See Address Specification for information on how to specify database links.

FieldSummaryTypeDCT DefaultReadWriteCA PP


At the core of the Calc record lies the CALC and RPCL fields. The CALC field contains the infix expresion which the record routine will use when it processes the record. The resulting value is placed in the VAL field and can be accessed from there. The CALC expression is actually converted to opcode and stored as Reverse Polish Notation in the RPCL field. It is this expression which is actually used to calculate VAL. The Reverse Polish expression is evaluated more efficiently during run-time than an infix expression. CALC can be changed at run-time, and a special record routine calls a function to convert it to Reverse Polish Notation.

The infix expressions that can be used are very similar to the C expression syntax, but with some additions and subtle differences in operator meaning and precedence. The string may contain a series of expressions separated by a semi-colon character ";" any one of which may actually provide the calculation result; however, all of the other expressions included must assign their result to a variable. All alphabetic elements described below are case independent, so upper and lower case letters may be used and mixed in the variable and function names as desired. Spaces may be used anywhere within an expression except between characters that make up a single expression element.

The range of expressions supported by the calculation record are separated into literals, constants, operands, algebraic operators, trigonometric operators, relational operators, logical operators, the assignment operator, parentheses and commas, and the question mark or '?:' operator.

FieldSummaryTypeDCT DefaultReadWriteCA PP
CALCCalculationSTRING [80]Yes YesYesYes
RPCLReverse Polish CalcNOACCESSNo NoNoNo




The expression uses the values retrieved from the INPx links as operands, though constants can be used as operands too. These values retrieved from the input links are stored in the A-L fields. The values to be used in the expression are simply referenced by the field letter. For instance, the value obtained from INPA link is stored in the field A, and the value obtained from INPB is stored in field B. The field names can be included in the expression which will operate on their respective values, as in A+B. Also, the RNDM nullary function can be included as an operand in the expression in order to generate a random number between 0 and 1.

FieldSummaryTypeDCT DefaultReadWriteCA PP
AValue of Input ADOUBLENo YesYesYes
BValue of Input BDOUBLENo YesYesYes
CValue of Input CDOUBLENo YesYesYes
DValue of Input DDOUBLENo YesYesYes
EValue of Input EDOUBLENo YesYesYes
FValue of Input FDOUBLENo YesYesYes
GValue of Input GDOUBLENo YesYesYes
HValue of Input HDOUBLENo YesYesYes
IValue of Input IDOUBLENo YesYesYes
JValue of Input JDOUBLENo YesYesYes
KValue of Input KDOUBLENo YesYesYes
LValue of Input LDOUBLENo YesYesYes

The keyword VAL returns the current contents of the VAL field (which can be written to by a CA put, so it might not be the result from the last time the expression was evaluated).

Algebraic Operators

Trigonometric Operators

Relational Operators

Logical Operators

Bitwise Operators

Assignment Operator

Parantheses, Comma, and Semicolon

The open and close parentheses are supported. Nested parentheses are supported.

The comma is supported when used to separate the arguments of a binary function.

The semicolon is used to separate expressions. Although only one traditional calculation expression is allowed, multiple assignment expressions are allowed.

Conditional Expression

The C language's question mark operator is supported. The format is: condition ? True result : False result

Expression Examples


A + B + 10


(A + B) < (C + D)

Question Mark

(A + B) < (C + D) ? E : F + L + 10

Prior to Base 3.14.9 it was legal to omit the : and the second (else) part of the conditional, like this:

(A + B)<(C + D) ? E

Result is E if (A + B)<(C + D)
Result is unchanged if (A + B)>=(C + D)

From 3.14.9 onwards, this expresion must be written as (A + B) < (C + D) ? E : VAL


A & B


sin(a); a:=a+D2R

Operator Display Parameters

These parameters are used to present meaningful data to the operator. These fields are used to display VAL and other parameters of the calculation record either textually or graphically.

The EGU field contains a string of up to 16 characters which is supplied by the user and which describes the values being operated upon. The string is retrieved whenever the routine get_units is called. The EGU string is solely for an operator's sake and does not have to be used.

The HOPR and LOPR fields only refer to the limits of the VAL, HIHI, HIGH, LOW and LOLO fields. PREC controls the precision of the VAL field.

See Fields Common to All Record Types for more on the record name (NAME) and description (DESC) fields.

FieldSummaryTypeDCT DefaultReadWriteCA PP
EGUEngineering UnitsSTRING [16]Yes YesYesNo
PRECDisplay PrecisionSHORTYes YesYesNo
HOPRHigh Operating RngDOUBLEYes YesYesNo
LOPRLow Operating RangeDOUBLEYes YesYesNo
NAMERecord NameSTRING [61]No YesNoNo
DESCDescriptorSTRING [41]Yes YesYesNo

Alarm Parameters

The possible alarm conditions for the Calc record are the SCAN, READ, Calculation, and limit alarms. The SCAN and READ alarms are called by the record support routines. The Calculation alarm is called by the record processing routine when the CALC expression is an invalid one, upon which an error message is generated.

The following alarm parameters which are configured by the user, define the limit alarms for the VAL field and the severity corresponding to those conditions.

The HYST field defines an alarm deadband for each limit.

See Alarm Specification for a complete explanation of record alarms and of the standard fields. Alarm Fields lists other fields related to alarms that are common to all record types.

FieldSummaryTypeDCT DefaultReadWriteCA PP
HIHIHihi Alarm LimitDOUBLEYes YesYesYes
HIGHHigh Alarm LimitDOUBLEYes YesYesYes
LOWLow Alarm LimitDOUBLEYes YesYesYes
LOLOLolo Alarm LimitDOUBLEYes YesYesYes
HHSVHihi SeverityMENU (menuAlarmSevr)Yes YesYesYes
HSVHigh SeverityMENU (menuAlarmSevr)Yes YesYesYes
LSVLow SeverityMENU (menuAlarmSevr)Yes YesYesYes
LLSVLolo SeverityMENU (menuAlarmSevr)Yes YesYesYes
HYSTAlarm DeadbandDOUBLEYes YesYesNo

Monitor Parameters

These paramaeters are used to determine when to send monitors for the value fields. These monitors are sent when the value field exceeds the last monitored field by the appropriate deadband, the ADEL for archiver monitors and the MDEL field for all other types of monitors. If these fields have a value of zero, everytime the value changes, monitors are triggered; if they have a value of -1, everytime the record is scanned, monitors are triggered. See "Monitor Specification" for a complete explanation of monitors.

FieldSummaryTypeDCT DefaultReadWriteCA PP
ADELArchive DeadbandDOUBLEYes YesYesNo
MDELMonitor DeadbandDOUBLEYes YesYesNo

Run-time Parameters

These fields are not configurable using a configuration tool and none are modifiable at run-time. They are used to process the record.

The LALM field is used to implement the hysteresis factor for the alarm limits.

The LA-LL fields are used to decide when to trigger monitors for the corresponding fields. For instance, if LA does not equal the value A, monitors for A are triggered. The MLST and ALST fields are used in the same manner for the VAL field.

FieldSummaryTypeDCT DefaultReadWriteCA PP
LALMLast Value AlarmedDOUBLENo YesNoNo
ALSTLast Value ArchivedDOUBLENo YesNoNo
MLSTLast Val MonitoredDOUBLENo YesNoNo
LAPrev Value of ADOUBLENo YesNoNo
LBPrev Value of BDOUBLENo YesNoNo
LCPrev Value of CDOUBLENo YesNoNo
LDPrev Value of DDOUBLENo YesNoNo
LEPrev Value of EDOUBLENo YesNoNo
LFPrev Value of FDOUBLENo YesNoNo
LGPrev Value of GDOUBLENo YesNoNo
LHPrev Value of HDOUBLENo YesNoNo
LIPrev Value of IDOUBLENo YesNoNo
LJPrev Value of JDOUBLENo YesNoNo
LKPrev Value of KDOUBLENo YesNoNo
LLPrev Value of LDOUBLENo YesNoNo

Record Support

Record Support Routines


For each constant input link, the corresponding value field is initialized with the constant value if the input link is CONSTANT or a channel access link is created if the input link is a PV_LINK.

A routine postfix is called to convert the infix expression in CALC to Reverse Polish Notation. The result is stored in RPCL.


See next section.


This is called if CALC is changed. special calls postfix.


Retrieves EGU.


Retrieves PREC.


Sets the upper display and lower display limits for a field. If the field is VAL, HIHI, HIGH, LOW, or LOLO, the limits are set to HOPR and LOPR, else if the field has upper and lower limits defined they will be used, else the upper and lower maximum values for the field will be used.


Sets the upper control and the lower control limits for a field. If the field is VAL, HIHI, HIGH, LOW, or LOLO, the limits are set to HOPR and LOPR, else if the field has upper and lower limits defined they will be used, else the upper and lower maximum values for the field type will be used.


Sets the following values:

upper_alarm_limit = HIHI

upper_warning_limit = HIGH

lower_warning_limit = LOW

lower_alarm_limit = LOLO

Record Processing

Routine process implements the following algorithm:

1. Fetch all arguments.
2. Call routine calcPerform, which calculates VAL from the postfix version of the expression given in CALC. If calcPerform returns success UDF is set to FALSE.
3. Check alarms. This routine checks to see if the new VAL causes the alarm status and severity to change. If so, NSEV, NSTA, and LALM are set. It also honors the alarm hysteresis factor (HYST). Thus the value must change by at least HYST before the alarm status and severity changes.
4. Check to see if monitors should be invoked.
5. Scan forward link if necessary, set PACT FALSE, and return.