Multi-Bit Binary Output Direct Record (mbboDirect)

The mbboDirect record performs roughly the opposite function to that of the mbbiDirect record.

It can accept boolean values in its 32 bit fields (B0-B9, BA-BF, B10-B19 and B1A-B1F), and converts them to a 32-bit signed integer in VAL which is provided to the device support. A zero value in a bit field becomes a zero bit in VAL, a non-zero value in a bit field becomes a one bit in VAL, with B0 being the least signficant bit and B1F the MSB/sign bit.

Parameter Fields

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

Scan Parameters

The mbboDirect record has the standard fields for specifying under what circumstances it will be processed. These fields are listed 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

Desired Output Parameters

Like all output records, the mbboDirect record must specify where its output should originate when it gets processed. The Output Mode SeLect field (OMSL) determines whether the output value should be read from another record or not. When set to closed_loop, a 32-bit integer value (the "desired output") will be read from a link specified in the Desired Output Link (DOL) field and placed into the VAL field.

When OMSL is set to supervisory, the DOL field is ignored during processing and the contents of VAL are used. A value to be output may thus be written direcly into the VAL field from elsewhere as long as the record is in supervisory mode.

FieldSummaryTypeDCT DefaultReadWriteCA PP
OMSLOutput Mode SelectMENU (menuOmsl)Yes YesYesYes
DOLDesired Output LinkINLINKYes YesYesNo
VALWordLONGYes YesYesYes

Bit Fields

The fields B0 through BF and B10 through B1F provide an alternative way to set the individual bits of the VAL field when the record is in supervisory mode. Writing to one of these fields will then modify the corresponding bit in VAL, and writing to VAL will update these bit fields from that value.

The VAL field is signed so it can be accessed through Channel Access as an integer; if it were made unsigned (a DBF_ULONG) its representation through Channel Access would become a double, which could cause problems with some client programs.

Prior to the EPICS release the individual bit fields were not updated while the record was in closed_loop mode with VAL being set from the DOL link, and writing to the bit fields in that mode could cause the record to process but the actual field values would not affect VAL at all. Changing the OMSL field from closed_loop to supervisory would set the bit fields from VAL at that time and trigger a monitor event for the bits that changed at that time. At record initialization if VAL is defined and the OMSL field is supervisory the bit fields would be set from VAL.

From EPICS the bit fields get updated from VAL during record processing and monitors are triggered on them in either mode. Attempts to write to the bit fields while in closed_loop mode will be rejected by the special() routine which may trigger an error from the client that wrote to them. During initialization if the record is still undefined (UDF) after DOL has been read and the device support initialized but at least one of the B0-B1F fields is non-zero, the VAL field will be set from those fields and UDF will be cleared.

FieldSummaryTypeDCT DefaultReadWriteCA PP
B0Bit 0UCHARYes YesYesYes
B1Bit 1UCHARYes YesYesYes
B2Bit 2UCHARYes YesYesYes
B3Bit 3UCHARYes YesYesYes
B4Bit 4UCHARYes YesYesYes
B5Bit 5UCHARYes YesYesYes
B6Bit 6UCHARYes YesYesYes
B7Bit 7UCHARYes YesYesYes
B8Bit 8UCHARYes YesYesYes
B9Bit 9UCHARYes YesYesYes
BABit 10UCHARYes YesYesYes
BBBit 11UCHARYes YesYesYes
BCBit 12UCHARYes YesYesYes
BDBit 13UCHARYes YesYesYes
BEBit 14UCHARYes YesYesYes
BFBit 15UCHARYes YesYesYes
B10Bit 16UCHARYes YesYesYes
B11Bit 17UCHARYes YesYesYes
B12Bit 18UCHARYes YesYesYes
B13Bit 19UCHARYes YesYesYes
B14Bit 20UCHARYes YesYesYes
B15Bit 21UCHARYes YesYesYes
B16Bit 22UCHARYes YesYesYes
B17Bit 23UCHARYes YesYesYes
B18Bit 24UCHARYes YesYesYes
B19Bit 25UCHARYes YesYesYes
B1ABit 26UCHARYes YesYesYes
B1BBit 27UCHARYes YesYesYes
B1CBit 28UCHARYes YesYesYes
B1DBit 29UCHARYes YesYesYes
B1EBit 30UCHARYes YesYesYes
B1FBit 31UCHARYes YesYesYes

Convert and Write Parameters

For records that are to write values to hardware devices, the OUT output link must contain the address of the I/O card, and the DTYP field must specify the proper device support module. Be aware that the address format differs according to the I/O bus used. See Address Specification for information on the format of hardware addresses.

During record processing VAL is converted into RVAL, which is the actual 32-bit word to be sent out. RVAL is set to VAL shifted left by the number of bits specified in the SHFT field (SHFT is normally set by device support). RVAL is then sent out to the location specified in the OUT field.

The fields NOBT and MASK can be used by device support to force some of the output bits written by that support to be zero. By default all 32 bits can be sent, but the NOBT field can be set to specify a smaller number of contiguous bits, or MASK can specify a non-contiguous set of bits. When setting MASK it is often necessary to set NOBT to a non-zero value as well, although in this case the actual value of NOBT may be ignored by the device support. If a device support sets the SHFT field it will also left-shift the value of MASK at the same time.

For mbboDirect records writing to a link instead of to hardware, the DTYP field must select one of the soft device support routines Soft Channel or Raw Soft Channel. The Soft Channel support writes the contents of the VAL field to the output link. The Raw Soft Channel support allows SHFT to be set in the DB file, and sends the result of ANDing the shifted MASK with the RVAL field's value.

FieldSummaryTypeDCT DefaultReadWriteCA PP
OUTOutput SpecificationOUTLINKYes YesYesNo
MASKHardware MaskULONGNo YesNoNo
NOBTNumber of BitsSHORTYes YesNoNo

Operator Display Parameters

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

FieldSummaryTypeDCT DefaultReadWriteCA PP
NAMERecord NameSTRING [61]No YesNoNo
DESCDescriptorSTRING [41]Yes YesYesNo

Run-time Parameters

These parameters are used by the run-time code for processing the mbbo Direct record.

MASK is used by device support routine to read the hardware register. Record support sets the low order NOBT bits of MASK at initialization, and device support is allowed to shift this value.

MLST holds the value when the last monitor for value change was triggered. OBIT has a similar role for bits held in the B0-B1F fields.

FieldSummaryTypeDCT DefaultReadWriteCA PP
NOBTNumber of BitsSHORTYes YesNoNo
ORAWPrev Raw ValueULONGNo YesNoNo
MASKHardware MaskULONGNo YesNoNo
MLSTLast Value MonitoredLONGNo YesNoNo
OBITLast Bit mask MonitoredLONGNo YesNoNo

Simulation Mode Parameters

The following fields are used to operate the record in simulation mode.

If SIMM (fetched through SIML) is YES, the record is put in SIMS severity and the value is written through SIOL, without conversion. SSCN sets a different SCAN mechanism to use in simulation mode. SDLY sets a delay (in sec) that is used for asynchronous simulation processing.

See Output Simulation Fields for more information on simulation mode and its fields.

FieldSummaryTypeDCT DefaultReadWriteCA PP
SIMLSimulation Mode LinkINLINKYes YesYesNo
SIMMSimulation ModeMENU (menuYesNo)No YesYesNo
SIOLSimulation Output LinkOUTLINKYes YesYesNo
SIMSSimulation Mode SeverityMENU (menuAlarmSevr)Yes YesYesNo
SDLYSim. Mode Async DelayDOUBLEYes-1.0YesYesNo
SSCNSim. Mode ScanMENU (menuScan)Yes65535YesYesNo

Alarm Parameters

The possible alarm conditions for mbboDirect records are the SCAN, READ, and INVALID alarms.

The IVOA field specifies an action to take when an INVALID alarm is triggered. There are three possible actions: Continue normally, Don't drive outputs, or Set output to IVOV. When Set output to IVOV is specified and a INVALID alarm is triggered, the record will write the value in the IVOV field to the output.

See Invalid Output Action Fields for more information about IVOA and IVOV.

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
IVOAINVALID outpt actionMENU (menuIvoa)Yes YesYesNo
IVOVINVALID output valueLONGYes YesYesNo

Record Support

Record Support Routines


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 its value and UDF is set to FALSE.

MASK is cleared and then the NOBT low order bits are set.

If device support includes init_record(), it is called.

If device support returns success, VAL is then set from RVAL and UDF is set to FALSE.


See next section.

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
      • Get value from DOL
      • Set PACT to FALSE
  3. Convert
    • If PACT is FALSE, compute RVAL
      • Set RVAL = VAL
      • Shift RVAL left SHFT bits
    • Status=write_mbboDirect
  4. 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.
  5. Check to see if monitors should be invoked.
    • Alarm monitors are invoked if the alarm status or severity has changed.
    • Archive and value change monitors are invoked if MLST is not equal to VAL.
    • Monitors for RVAL and RBV are checked whenever other monitors are invoked.
    • NSEV and NSTA are reset to 0.
  6. Scan forward link if necessary, set PACT FALSE, and return.

Device Support

Fields Of Interest To Device Support

Each mbboDirect record must have an associated set of device support routines. The primary responsibility of the device support routines is to obtain a new raw mbbo value whenever write_mbboDirect is called. The device support routines are primarily interested in the following fields:

FieldSummaryTypeDCT DefaultReadWriteCA PP
PACTRecord activeUCHARNo YesNoNo
NSEVNew Alarm SeverityMENU (menuAlarmSevr)No YesNoNo
NSTANew Alarm StatusMENU (menuAlarmStat)No YesNoNo
NOBTNumber of BitsSHORTYes YesNoNo
OUTOutput SpecificationOUTLINKYes YesYesNo
RBVReadback ValueULONGNo YesNoNo
MASKHardware MaskULONGNo YesNoNo

Device Support Routines

Device support consists of the following routines:

long report(int level)

This optional routine is called by the IOC command dbior and is passed the report level that was requested by the user. It should print a report on the state of the device support to stdout. The level parameter may be used to output increasingly more detailed information at higher levels, or to select different types of information with different levels. Level zero should print no more than a small summary.

long init(int after)

This optional routine is called twice at IOC initialization time. The first call happens before any of the init_record() calls are made, with the integer parameter after set to 0. The second call happens after all of the init_record() calls have been made, with after set to 1.



This routine is optional. If provided, it is called by the record support init_record() routine. If MASK is used, it should be shifted if necessary and SHFT given a value.


  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.



This routine must output a new value. It returns the following values:

Device Support For Soft Records

This SOft Channel module writes the current value of VAL.

If the OUT link type is PV_LINK, then dbCaAddInlink is called by init_record().

write_mbboDirect calls recGblPutLinkValue to write the current value of VAL.

See Soft Output.