NB: This manual documents a 20+ year old version of EPICS, see here for the EPICS 7 Record Reference documentation.

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EPICS Record Reference Manual

Chapter 20: mbbiDirect - Multi-Bit Binary Input Direct

Johnny Tang, Matthew Bickley, and Chip Watson

Continuous Electron Beam Accelerator Facility

Southeastern Universities Research Association

1. Introduction

The mbbiDirect record retrieves a sixteen-bit hardware value and converts it to an array of sixteen unsigned characters, each representing a bit of the word. These fields (B0-B9, BA-BF) are set to 1 if a bit is set, and 0 if not.

This record's operation is similar to that of the multi-bit binary input record, and it has many fields in common with it. This record also has two available soft device support modules--Soft Channel and Raw Soft Channel. The fields fall into the following categories:

scan parameters

read and convert parameters

operator display parameters

alarm parameters

run-time and simulation mode parameters

2. Scan fields

The mbbiDirect 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. Read and Convert fields

The device support routines obtain the record's input from the device or link specified in the INP field. For records that obtain their input from devices, the INP field 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, 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.

Two soft device support modules can be specified in DTYP--Soft Channel and Raw Soft Channel. Raw Soft Channel reads the value into RVAL, upon which the normal conversion process is undergone. Soft Channel reads any unsigned integer directly into VAL. For a soft mbbiDirect record, the INP field can be a constant, a database, or a channel access link. If INP is a constant, then the VAL is initialized to the INP value but can be changed at run-time via dbPutField or dbPutLink. See Address Specification, Chapter 1, 2, for information on how to database links.

For records that don't use Soft Channel device support, RVAL is used to determine VAL as follows:

1. RVAL is assigned to a temporary variable--rval = RVAL

2. rval is shifted right SHFT number of bits.

3. VAL is set equal to rval.

Each of the fields, B0-BF, represents one bit of the word.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
VALValue FieldENUMNo0YesYesYesYes
RVALRaw Data ValueULONGNo0YesYesYesYes
B0Bit 0 ValueUCHARYes0YesYesYesYes
B1Bit 1 ValueUCHARYes0YesYesYesYes
B2Bit 2 ValueUCHARYes0YesYesYesYes
B3Bit 3 ValueUCHARYes0YesYesYesYes
B4Bit 4 ValueUCHARYes0YesYesYesYes
B5Bit 5 ValueUCHARYes0YesYesYesYes
B6Bit 6 ValueUCHARYes0YesYesYesYes
B7Bit 7 ValueUCHARYes0YesYesYesYes
B8Bit 8 ValueUCHARYes0YesYesYesYes
B9Bit 9 ValueUCHARYes0YesYesYesYes
BABit 10 ValueUCHARYes0YesYesYesYes
BBBit 12 ValueUCHARYes0YesYesYesYes
BCBit 13 ValueUCHARYes0YesYesYesYes
BDBit 14 ValueUCHARYes0YesYesYesYes
BEBit 15 ValueUCHARYes0YesYesYesYes
BFBit 16 ValueUCHARYes0YesYesYesYes

4. Operator Display Parameters

These parameters are used to present meaningful data to the operator.

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

5. Alarm Parameters

The possible alarm conditions for multi-bit binary input direct records are the SCAN and READ alarms. These alarms are not configurable by the user since they are always of MAJOR severity. See Alarm Specification, Chapter 1, 4, for a complete explanation of Scan and Read alarms. No fields exist for the mbbi direct record to have state alarms.

Alarm Fields, Chapter 2, 3, lists other fields related to a alarms that are common to all record types.

6. Run-time and Simulation Mode Fields

These parameters are used by the run-time code for processing the mbbi direct record. They are not configurable prior to run-time.

MASK is used by device support routine to read hardware register. Record support sets low order NOBT bits in MASK. Device support can shift this value.

The LALM field implements the change of state alarm severity by holding the value of VAL when the previous change of state alarm was issued.

MLST holds the value when the last monitor for value change was triggered.

SDEF is used by record support to save time if no states are defined.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
NOBTNumber of BitsSHORTYes0YesNoNoNo
LALMLast AlarmedUSHORTNo0YesNoNoNo
MLSTMonitor LastUSHORTNo0YesNoNoNo
SDEFStates Defined?SHORTNo0YesNoNoNo

The following fields are used to operate the mbbiDirect record 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

7. Record Support Routines


This routine initializes SIMM with the value of SIML if SIML type is CONSTANT link or creates a channel access link if SIML type is PV_LINK. SVAL is likewise initialized if SIOL is CONSTANT or PV_LINK.

This routine next checks to see that device support is available and a device support read routine is defined. If either does not exist, an error message is issued and processing is terminated.

Clears MASK and then sets the NOBT low order bits.

If device support includes init_record, it is called.

refresh_bits is then called to refresh all the bit fields based on a hardware value.


See next section.


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

8. 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. readValue is called. See Output Records, Chapter 3, 3, for information.

3. If PACT has been changed to TRUE, the device support read routine has started but has not completed reading a new input value. In this case, the processing routine merely returns, leaving PACT TRUE.

4. Convert.

5. Check to see if monitors should be invoked.

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

9. Device Support

9.1. Fields Of Interest To Device Support

Each input record must have an associated set of device support routines.

The primary responsibility of the device support routines is to obtain a new raw input value whenever read_mbbiDirect is called. The device support routines are primarily interested in the following fields:
PACTProcessing ActiveSee Chapter 2, Fields Common to All Record Types for an explanation of these fields.
DPVTDevice Private
UDFVAL Undefined
NSEVNew Alarm Severity
NSTANew Alarm Status
NOBTNumber of BitsNumber of hardware bits accessed. They must be consecutive.
VALValue FieldThis field is set by the device support routines if they don't want record support to set it.
INPInput LinkThis field is used by the device support routines to locate its input.
RVALRaw Data ValueIt is the responsibility of the device support routine to give this field a value.
MASKMaskThis is a mask used to read the hardware. Record support sets the low order NOBT bits. The device support routine can shift the bits. The device support routine should perform the shift in init_record.
SHFTShiftThis can be set by the device support module at init_record time.

9.2. Device Support Routines

Device support consists of the following routines:


  report(FILE fp, paddr)
Not currently used.


This routine is called once during IOC initialization.


This routine is optional. If provided, it is called by the record support init_record routine. If it uses MASK, it should shift it as necessary and also give SHFT 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 provide a new input value. It returns the following values:

9.3. Device Support For Soft Records

Two soft device support modules, Soft Channel and Raw Soft Channel, are provided for multi-bit binary input direct records not related to actual hardware devices. The INP link type must be either CONSTANT, DB_LINK, or CA_LINK.

Soft Channel

For this module, read_mbbiDirect always returns a value of 2, which means that no conversion is performed.

If the INP link type is constant, then the constant value is stored into VAL by init_record, and UDF is set to FALSE. VAL can be changed via dbPut requests. If the INP link type is PV_LINK, then dbCaAddInlink is called by init_record.

read_mbbiDirect calls recGblGetLinkValue to read the current value of VAL.

See Input Records, Chapter 3, 2, for a further explanation.

If the return status of recGblGetLinkValue is zero, then read_mbbi sets UDF to FALSE. The status of recGblGetLinkValue is returned.

Raw Soft Channel

This module is like the previous except that values are read into RVAL, VAL is computed from RVAL, and read_mbbiDirect returns a value of 0. Thus the record processing routine will determine VAL in the normal way.

1. - Introduction
2. - Scan fields
3. - Read and Convert fields
4. - Operator Display Parameters
5. - Alarm Parameters
6. - Run-time and Simulation Mode Fields
7. - Record Support Routines
8. - Record Processing
9. - Device Support
9.1. - Fields Of Interest To Device Support
9.2. - Device Support Routines
9.3. - Device Support For Soft Records
Soft Channel
Raw Soft Channel

EPICS Record Reference Manual - 19 MAY 1998
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