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EPICS Record Reference Manual

Chapter 19: mbbi -- Multi-Bit Binary Input

1. Introduction

The normal use for the multi-bit binary input record is to read multiple bit inputs from hardware. The binary value represents a state from a range of up to 16 states. The multi-bit input record interfaces with devices that use more than one bit.

Most device support modules obtain values from hardware and place the value in RVAL. For these device support modules record processing uses RVAL to determine the current state (VAL is given a value between 0 and 15). Device support modules may optionally read a value directly into VAL.

Soft device modules are provided to obtain input via database or channel access links or via dbPutField or dbPutLink requests. Two soft device support modules are provided: Soft Channel allows VAL to be an arbitrary unsigned short integer. Raw Soft Channel reads the value into RVAL just like normal device support modules.

The multi-bit binary input 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 parameters

The multi-bit binary input record has the standard fields for specifying under what circumstances it 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 Parameters

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 mbbi 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 constant value but can be changed at run-time via dbPutField or dbPutLink. See Address Specification, Chapter 1, 2, for information on the format of database addresses.

Unless the device support routine specifies no conversion, 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. A match is sought between rval and one of the state value fields, ZRVL-FFVL.

Each of the fields, ZRVL-FFVL, represents one of the possible sixteen states (not all sixteen have to be used).

Alternatively, the input value can be read as a string, in which case, a match is sought with one of the strings specified in the ZRST-FFST fields. Then RVAL is set equal to the corresponding value for that string, and the conversion process occurs.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
VALValue FieldENUMNo0YesYesYesYes
RVALRaw Data ValueULONGNo0YesYesYesYes
ZRVLZero ValueULONGYes0YesYesNoYes
ONVLOne valueULONGYes0YesYesNoYes
TWVLTwo ValueULONGYes0YesYesNoYes
THVLThree ValueULONGYes0YesYesNoYes
FRVLFour ValueULONGYes0YesYesNoYes
FVVLFive ValueULONGYes0YesYesNoYes
SXVLSix ValueULONGYes0YesYesNoYes
SVVLSeven ValueULONGYes0YesYesNoYes
EIVLEight valueULONGYes0YesYesNoYes
NIVLNine ValueULONGYes0YesYesNoYes
TEVLTen ValueULONGYes0YesYesNoYes
ELVLEleven ValueULONGYes0YesYesNoYes
TVVLTwelve ValueULONGYes0YesYesNoYes
TTVLThirteen ValueULONGYes0YesYesNoYes
FTVLFourteen ValueULONGYes0YesYesNoYes
FFVLFifteen ValueULONGYes0YesYesNoYes
ZRSTZero StringSTRING [16]YesNullYesYesNoYes
ONSTOne StringSTRING [16]YesNullYesYesNoYes
TWSTTwo StringSTRING [16]YesNullYesYesNoYes
THSTThree StringSTRING [16]YesNullYesYesNoYes
FRSTFour StringSTRING [16]YesNullYesYesNoYes
FVSTFive StringSTRING [16]YesNullYesYesNoYes
SXSTSix StringSTRING [16]YesNullYesYesNoYes
SVSTSeven StringSTRING [16]YesNullYesYesNoYes
EISTEight StringSTRING [16]YesNullYesYesNoYes
NISTNine StringSTRING [16]YesNullYesYesNoYes
TESTTen StringSTRING [16]YesNullYesYesNoYes
ELSTEleven StringSTRING [16]YesNullYesYesNoYes
TVSTTwelve StringSTRING [16]YesNullYesYesNoYes
TTSTThirteen StringSTRING [16]YesNullYesYesNoYes
FTSTFourteen StringSTRING [16]YesNullYesYesNoYes
FFSTFifteen StringSTRING [16]YesNullYesYesNoYes

4. Operator Display Parameters

These parameters are used to present meaningful data to the operator. They display the value and other parameters of the mbbi record either textually or graphically. The ZRST-FFST fields contain strings describing one of the possible states of the record. The get_enum_str and get_enum_strs record routines retrieve these strings for the operator. Get_enum_str gets the string corresponding to the value set in VAL, and get_enum_strs retrieves all the strings.

See Chapter 2, Fields Common to All Record Types, for more on the record name (NAME) and description (DESC) fields.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
ZRST,...,FFSTZero String, One String, ...STRING [16]YesNullYesYesNoYes
HOPRHigh Operating RangeFLOATYes0YesYesNoNo
NAMERecord NameSTRING [29]Yes0YesNoNo 
DESCDescriptionSTRING [29]YesNullYesYesNoNo

5. Alarm Parameters

The possible alarm conditions for multi-bit binary inputs are the SCAN, READ, and state alarms. The state alarms are configured in the below severity fields. These fields have the usual possible values for severity fields: NO ALARM, MINOR, and MAJOR.

The unknown state severity (UNSV) field, if set to MINOR or MAJOR, triggers an alarm when the record support routine cannot find a matching value in the state value fields for rval.

The change of state severity (COSV) field triggers an alarm when any change of state occurs, if set to MAJOR or MINOR.

The other fields, when set to MAJOR or MINOR, trigger an alarm when VAL equals the corresponding state. See the See Alarm Specification, Chapter 1, 4, for a complete explanation of discrete alarms and these fields. Alarm Fields, Chapter 2, 3, lists other fields related to a alarms that are common to all record types.
FieldSummaryTypeDCTInitialAccessModifyRec Proc MonitorPP
UNSVUnknown State SeverityGBLCHOICEYes0YesYesNoYes
COSVChange of State SeverityGBLCHOICEYes0YesYesNoYes
ZRSV0 State SeverityGBLCHOICEYes0YesYesNoYes
ONSV1 State SeverityGBLCHOICEYes0YesYesNoYes
TWSV2 State SeverityGBLCHOICEYes0YesYesNoYes
THSV3 State SeverityGBLCHOICEYes0YesYesNoYes
FRSV4 State SeverityGBLCHOICEYes0YesYesNoYes
FVSV5 State SeverityGBLCHOICEYes0YesYesNoYes
SXSV6 State SeverityGBLCHOICEYes0YesYesNoYes
SVSV7 State SeverityGBLCHOICEYes0YesYesNoYes
EISV8 State SeverityGBLCHOICEYes0YesYesNoYes
NISV9 State SeverityGBLCHOICEYes0YesYesNoYes
TESV10 State SeverityGBLCHOICEYes0YesYesNoYes
ELSV11 State SeverityGBLCHOICEYes0YesYesNoYes
TVSV12 State SeverityGBLCHOICEYes0YesYesNoYes
TTSV13 State SeverityGBLCHOICEYes0YesYesNoYes
FTSV14 State SeverityGBLCHOICEYes0YesYesNoYes
FFSV15 State SeverityGBLCHOICEYes0YesYesNoYes

6. Run-time and Simulation Mode Parameters

These parameters are used by the run-time code for processing the multi-bit binary input.

MASK is used by device support routine to read the hardware register. It is shifted left NOBT bits by the record processing routine. The user can configure the NOBT field, but the device support routines may set it, in which case the value given to it by the user is simply overridden.

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 mbbi 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.

init_common is then called to determine if any states are defined. If states are defined, SDEF is set to TRUE.


See next section.


Calls init_common to compute SDEF when any of the fields ZRVL, ... FFVL change value.


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


Retrieves ASCII string corresponding to VAL.


Retrieves ASCII strings for ZRST,...FFST.


Checks if string matches ZRST,...FFST and if it does, sets 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 Input Records, Chapter 3, 2 for more 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 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.

6. Check to see if monitors should be invoked.

7. 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_mbbi 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 I/O Event 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 records not related to actual hardware devices. The INP link type must be either CONSTANT, DB_LINK, or CA_LINK.

Soft Channel

read_mbbi 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_mbbi calls recGblGetLinkValue to read the current value of VAL. See Soft Input, Chapter 3, 2.3.

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_mbbi returns a value of 0. Thus the record processing routine will determine VAL in the normal way.

1. - Introduction
2. - Scan parameters
3. - Read and Convert Parameters
4. - Operator Display Parameters
5. - Alarm Parameters
6. - Run-time and Simulation Mode Parameters
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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