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EPICS Record Reference Manual

Chapter 8: bo--Binary Output

1. Introduction


The normal use for this record type is to store a simple bit (0 or 1) value to be sent to a Digital Output module. It can also be used to write binary values into other records via database or channel access links. This record can implement both latched and momentary binary outputs depending on how the HIGH field is configured.

The binary output's fields fall into the following categories:

scan parameters

convert and write parameters

operator display parameters

alarm parameters

run-time parameters

2. Scan Parameters


The binary output record has the standard fields for specifying under what circumstances the record will be processed. These fields are listed in Scan Fields, Chapter 2, 2. In addition, Scanning Specification, Chapter 1, 1, explains how these fields are used. Note that I/O event scanning is only supported for those card types that interrupt.

3. Desired Output Parameters


The binary output record must specify where its desired output originates. The desired output needs to be in engineering units.

The first field that determines where the desired output originates is the output mode select (OSML) field, which can have two possible values--closed loop or supervisory. If supervisory is specified, the value in the VAL field can be set externally via dbPuts at run-time. If closed loop is specified, the VAL field's value is obtained from the address specified in the desired output location (DOL) field which can be either a database link or a channel access link. To achieve continuous control, a database link to a control algorithm record should be entered in the DOL field. Address Specification, Chapter 1, 2, presents more information on database addresses and links. Scanning Specification, Chapter 1, 1, explains the effect of database linkage on scanning.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
DOLDesired Output Location (Input Link)INLINKYes0NoNoN/ANo
OMSLOutput Mode SelectGBLCHOICEYes0YesYesNoNo

4. Convert and Write Parameters


These parameters are used to determine where the binary output writes to and how to convert the engineering units to a raw signal. After VAL is set and forced to be either 1 or 0, as the result of either a dbPut or a new value being retrieved from the link in the DOL field, then what happens next depends on which device support routine is used and how the HIGH field is configured.

If the Soft Channel device support routine is specified, then the device support routine writes the VAL field's value to the address specified in the OUT field. Otherwise, RVAL is the value finally written by the device support routines after being converted.

If VAL is equal to 0, then the record processing routine sets RVAL equal to zero. When VAL is not equal to 0, then RVAL is set equal to the value contained in the MASK field. (MASK is set by the device support routines and is of no concern to the user.) Also when VAL is not 0 and after RVAL is set equal to MASK, the record processing routine checks to see if the HIGH field is greater than 0. If it is, then the routine will process the record again with VAL set to 0 after the number of seconds specified by HIGH. Thus, HIGH implements a momentary output which changes the state of the device back to 0 after N number of seconds.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
DTYPDevice TypeDEVCHOICEYes0YesNoNo 
OUTOutput LinkOUTLINKYes0NoNoN/ANo
VALValue FieldENUMNo0YesYesYesYes
RVALRaw Data ValueULONGNo0YesYesYesYes
HIGHSeconds to Hold HighFLOATYes0YesYesNoNo
ZNAMZero NameSTRING [20]YesNullYesYesNoYes
ONAMOne NameSTRING [20]YesNullYesYesNoYes

4.1. Conversion Parameters

The ZNAM field has the string that corresponds to the 0 state, and the ONAM field holds the string that corresponds to the 1 state. These fields, other than being used to tell the operator what each state represents, are used to perform conversions if the value fetched by DOL is a string. If it is, VAL is set to the state correspond to that string. For instance, if the value fetched is the string "Off" and the ZNAM string is "Off," then VAL is set to 0.

After VAL is set, if VAL is equal to 0, then the record processing routine sets RVAL equal to zero. When VAL is not equal to 0, then RVAL is set equal to the value contained in the MASK field. (MASK is set by the device support routines and is of no concern to the user.) Also when VAL is equal to 1 and after RVAL is set equal to MASK, the record processing routine checks to see if the HIGH field is greater than 0. If it is, then the routine process the record again with VAL=0 after the number of seconds specified by HIGH. Thus, HIGH implements a latched output which changes the state of the device or link to 1, then changes it back to 0 after N number of seconds.
ZNAMASCII string defining state zero
ONAMASCII string defining state one
HIGHIf this value is greater than zero, then whenever VAL is set equal to 1, it is reset to zero after HIGH seconds.

4.2. Output Specification

The OUT field specifies where the binary output record gets its input. It must specify the address of an I/O card if the record sends its output to hardware, and the DTYP field must contain a the corresponding device support module. Be aware that the address format differs according to the I/O bus used. See Address Specification, Chapter 1, 2, for information on the format of hardware addresses. You can see a list of the device support modules currently supported at the user's local site by using the dbst utility in R3.13.

Otherwise, if the record is configured to use the soft device support modules, then it can be either a database link, a channel access link, or a constant. Be aware that nothing will be written when OUT is a constant. See Address Specification, Chapter 1, 2, for information on the format of database and channel access addresses. Also, see Section 10.3, Device Support For Soft Records, in this chapter for more on output to other records.

5. Operator Display Parameters


These parameters are used to present meaningful data to the operator. The get_enum_str record support routine can retrieve the state string corresponding to the VAL's state. So if the value is 1, get_enum_str will return the string in the ONAM field; and if 0, get_enum_str will return the ZNAM string.

See Chapter 2, Fields Common to All Record Types, for more on the record name (NAME) and description (DESC) fields.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
ZNAMZero NameSTRING [20]YesNullYesYesNoYes
ONAMOne NameSTRING [20]YesNullYesYesNoYes
NAMERecord NameSTRING [29]Yes0YesNoNoNo
DESCDescriptionSTRING [29]YesNullYesYesNoNo

6. Alarm Parameters


These parameters are used to determine the binary output's alarm condition and to determine the severity of that condition. The possible alarm conditions for binary outputs are the SCAN, READ , INVALID, and state alarms. The user can configure the state alarm conditions using these fields.

The possible values for these fields are NO_ALARM, MINOR, and MAJOR. The ZSV holds the severity for the zero state; OSV for the one state. COSV is used to cause an alarm whenever the state changes between the states (0-1, or 1-0) and its severity is configured as MINOR or MAJOR.

See Invalid Alarm Output Action, Chapter 3, 3.5, for more information on the IVOA and IVOV fields. Alarm Fields, Chapter 2, 3, lists other fields related to a alarms that are common to all record types.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
ZSVZero SeverityGBLCHOICEYes0YesYesNoYes
OSVOne SeverityGBLCHOICEYes0YesYesNoYes
COSVChange of State SeverityGBLCHOICEYes0YesYesNoYes
IVOAInvalid AlarmGBLCHOICEYes0YesYesNoNo
IVOVInvalid Alarm Output ValueUSHORTYes0YesYesNoNo

7. Run-Time and Simulation Mode Parameters


These parameters are used by the run-time code for processing the binary output. They are not configurable using a configuration tool. They represent the current state of the binary output.

ORAW is used to determine if monitors should be triggered for RVAL at the same time they are triggered for VAL.

MASK is given a value by the device support routines and should not concern the user.

The RBV field is also set by device support. It is the actual read back value obtained from the hardware itself or from the associated device driver. The ORBV field is used to decide if monitors should be triggered for RBV at the same time monitors are triggered for changes in VAL.

The LALM field holds the value of the last occurrence of the change of state alarm. It is used to implement the change of state alarm, and thus only has meaning if COSV is MINOR or MAJOR.

The MLST is used by the process record support routine to determine if archive and value change monitors are invoked. They are if MLST is not equal to VAL.

The WPDT field is a private field for honoring seconds to hold HIGH.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
ORAWOld Raw ValueULONGNo0YesNoNoNo
MASKHardware MaskULONGNocomputeYesNoNoNo
RBVReadback ValueULONGNo0YesNoNoNo
ORBVOld Readback ValueULONGNo0YesNoNoNo
LALMLast Alarmed ValueUSHORTNo0YesNoNoNo
MLSTLast Monitored ValueUSHORTNo0YesNoNoNo
RPVTRecord PrivateNOACCESSNo0NoNoNoNo
WDPTWatchdog PointerNOACCESSNo0NoNoNoNo

The following fields are used to operate the binary output in the simulation mode. See Chapter 3, Fields Common to Many Record Types, for more information on these fields.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
SIOLSimulation Value LocationINLINKYes0NoNoN/ANo
SVALSimulation ValueDOUBLENo0YesYesNoNo
SIMLSimulation Mode LocationINLINKYes0NoNoN/ANo
SIMMSimulation ModeGBLCHOICENo0YesYesNoNo
SIMSSimulation Mode Alarm SeverityGBLCHOICEYes0YesYesNoNo

8. Record Support Routines


init_record

This routine initializes SIMM if SIML is a constant or creates a channel access link if SIML is PV_LINK. If SIOL is PV_LINK a channel access link is created .

This routine next checks to see that device support is available. The routine next checks to see if the device support write routine is defined.

If either device support or the device support write routine does not exist, an error message is issued and processing is terminated.

If DOL is a constant, then VAL is initialized to 1 if its value is nonzero or initialized to 0 if DOL is zero, and UDF is set to FALSE.

If device support includes init_record, it is called. VAL is set using RVAL, and UDF is set to FALSE.

process

See next section.

get_value

Fills in the values of struct valueDes so that they refer to VAL.

get_enum_str

Retrieves ASCII string corresponding to VAL.

get_enum_strs

Retrieves ASCII strings for ZNAM and ONAM.

put_enum_str

Checks if string matches ZNAM or ONAM, and if it does, sets VAL.

9. Record Processing


Routine process implements the following algorithm:

1. Check to see that the appropriate device support module exists. If it doesn't, an error message is issued and processing is terminated with the PACT field still set to TRUE. This ensures that processes will no longer be called for this record. Thus error storms will not occur.

2. If PACT is 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.

4. Check severity and write the new value. See Invalid Alarm Output Action, Chapter 3, 3.5, for more information on how INVALID alarms affect output.

5. If PACT has been changed to TRUE, the device support write output routine has started but has not completed writing the new value. In this case, the processing routine merely returns, leaving PACT TRUE.

6. Check WAIT. If VAL is 1 and WAIT is greater than 0, process again with a VAL=0 after WAIT seconds.

7. Check to see if monitors should be invoked.

8. Scan forward link if necessary, set PACT FALSE, and return.

10. Device Support


10.1. Fields Of Interest To Device Support

Each binary output record must have an associated set of device support routines. The primary responsibility of the device support routines is to write a new value whenever write_bo is called. The device support routines are primarily interested in the following fields:
NameSummaryDescription
PACTProcessing ActiveSee Chapter 2, Fields Common to All Record Types for an explanation of these fields.
DPVTDevice Private
NSEVNew Alarm Severity
NSTANew Alarm Status
VALValue FieldThis field is only of interest to device support routines that do not use MASK and RVAL.
OUTOutput LinkThis field is used by the device support routines to locate its output.
RVALRaw Data ValueIf MASK is defined then record support sets RVAL=(0,MASK) if VAL is (0, not zero).
MASKHardware mask.The device support module must set this field. Not that if VAL is 1, then record processing sets RVAL = MASK.
RBVRead Back ValueThis is the actual read back value obtained from the hardware itself or from the associated device driver. It is the responsibility of the device support routine to give this field a value.

10.2. Device Support routines

Device support consists of the following routines:

report

  report(FILE fp, paddr)
Not currently used.

init

  init()
This routine is called once during IOC initialization.

init_record

  init_record(precord)
This routine is optional. If provided, it is called by the record support init_record routine. It should determine MASK if it is needed.

get_ioint_info

  get_ioint_info(int cmd,struct dbCommon *precord,IOSCANPVT *ppvt)
This routine is called by the ioEventScan system each time the record is added or deleted from an I/O event scan list. cmd has the value (0,1) if the record is being (added to, deleted from) an I/O event list. It must be provided for any device type that can use the ioEvent scanner.

write_bo

  write_bo(precord)
This routine must output an new value. It returns the following values:

10.3. Device Support For Soft Records

Two soft device support modules Soft Channel and Raw Soft Channel are provided for output records not related to actual hardware devices. The OUT link type must be either a CONSTANT, DB_LINK, or CA_LINK.

Soft Channel

This module writes the current value of VAL.

If the OUT link type is PV_LINK, then dbCaAddInlink is called by init_record. init_record always returns a value of 2, which means that no conversion will ever be attempted. write_bo calls recGblPutLinkValue to write the current value of VAL. See Soft Output, Chapter 3, 3.2, for details.

Raw Soft Channel

This module is like the previous except that it writes the current value of RVAL.

1. - Introduction
2. - Scan Parameters
3. - Desired Output Parameters
4. - Convert and Write Parameters
4.1. - Conversion Parameters
4.2. - Output Specification
5. - Operator Display Parameters
6. - Alarm Parameters
7. - Run-Time and Simulation Mode Parameters
8. - Record Support Routines
init_record
process
get_value
get_enum_str
get_enum_strs
put_enum_str
9. - Record Processing
10. - Device Support
10.1. - Fields Of Interest To Device Support
10.2. - Device Support routines
report
init
init_record
get_ioint_info
write_bo
10.3. - Device Support For Soft Records
Soft Channel
Raw Soft Channel

EPICS Record Reference Manual - 19 MAY 1998
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