CNTLUNIT

CNTLUNIT is an optional statement that describes the following:
  • The characteristics of the control unit
  • The channel paths to which the control unit is attached
  • The unit addresses the control unit recognizes.

Each physical control unit in the I/O configuration must be specified in a separate CNTLUNIT statement to be used. This requirement includes control units that reside in the same physical unit as an I/O device or in another control unit.

You are recommended to define only one CNTLUNIT statement for each physical control unit, control unit image (defined with CUADD values), or control-unit function in your configuration. However, there are configurations that require you to use multiple CNTLUNIT statements:
  • Some storage controls (for example, the IBM 3990) contain multiple control-unit functions with the number varying based on the mode of the storage control (for example, DLS or DLSE in the 3990 model 3). You are recommended to code a CNTLUNIT statement for each control-unit function (storage director) provided in the storage control.
  • You might require multiple logical partitions (LPs) to access a single control unit, perhaps with multiple paths per LP. In this case, try to use shared channel paths to a single control unit definition. However, if doing so is not possible (for example, if the configuration calls for more than eight paths to a parallel control unit), you can use multiple CNTLUNIT statements to define the single control unit function. In this case, ensure that each LP does not have paths defined to more than one CNTLUNIT definition.
  • If your control unit supports both ESCON and parallel interfaces, you might want to use both types of interfaces to the same LP. You are recommended to avoid this type of configuration, but if you require the mixing of interfaces, you must consider the following rules:
    • You must choose between all-parallel or all-ESCON interfaces to any one LP at any one time. You can use one CNTLUNIT statement to define a control-unit image for the parallel paths and another CNTLUNIT statement to define a control-unit image for the ESCON paths. Each CNTLUNIT must be accompanied with unique IODEVICE statements.
    • When using the ESCON paths to the control unit, you must:
      • Vary offline all devices (that is, device numbers) defined to the parallel control-unit image.
      • Disable the parallel interfaces at the physical control unit.
    • When using the parallel paths, vary offline all devices (that is, device numbers) defined to the ESCON control-unit image by doing one of the following tasks:
      • If you have an ESCON Director, use the ESCON Manager (or the ESCON Director console) to prohibit the connection between the control unit and the system
      • If your ESCON connections are point-to-point, configure the chpids offline using the operating system, ESCON Manager or the CPC console.
    • When you are running VM with guest operating systems, you can use multiple CNTLUNIT statements for a single physical control unit in certain environments to effectively dedicate the same physical devices to more than one guest. This technique involves potential path-grouping considerations that create operational complications. Ensure you have determined possible consequences and that you use caution if employing this technique.
See Machine limits and rules for a list of machine limits and rules for your CPC. See List of I/O devices and control units for a list of some control unit types and their characteristics.
Based on information in the CNTLUNIT statements, IOCP constructs control unit headers for a logical channel subsystem (CSS) to use. A control unit header is a logical representation of one to eight physical control units. A control unit header is built for each one of the following units:
  • Physical control unit with no I/O devices attached.
  • Physical control unit that does not share any I/O devices with other physical control units.
  • Groups of two or more control units that share devices between them.

A CSS uses the control unit headers for queuing I/O requests for the devices attached to the associated physical control units. One I/O request queue exists for each control unit header. A CSS adds to the same I/O request queue all I/O requests for all devices in the control unit header. (Devices in the control unit header are all the devices attached to the set of physical control units that are in the control unit header.)

IOCP also establishes a rotation order for the channel paths associated with each control unit header. When initiating I/O requests associated with the control unit header, a CSS uses this rotation order to determine the sequence for selecting channel paths. See Rotation order for a description of how IOCP establishes the rotation order of the channel paths.

The CNTLUNIT statement must follow any CHPID statements that specify channel paths the control unit uses. The CNTLUNIT statement must precede any IODEVICE statements that refer to the control unit.

See Coding IOCP statements for a summary of the rules for coding statements and the notation used in this document to illustrate statements.

The format of the CNTLUNIT statement is as follows:
 [symbol]      CNTLUNIT      CUNUMBR=number
                             PATH=((CSS(cssid),chpid[,chpid]...),...) 
                             [LINK=((CSS(cssid),link address          
                                  [,link address]...),...)] 
                             [CUADD=address] 
                             [PROTOCL={D|S|S4}] 
                             SHARED={Y|N} 
                             UNIT=type 
                             UNITADD=((address[,number]),...) 
CUNUMBR=number
Specifies the hexadecimal number that is assigned to the control unit. One to four hexadecimal digits in the range of 0000-FFFE can be specified. You must assign a unique number to each control unit. The numbers can be assigned arbitrarily.
PATH=
cssid
Specifies the logical channel subsystem (CSS) IDs associated with this parameter. A CSS ID is a 1-digit number in the range 0-n. See Table 2 to determine the maximum CSS ID your CPC supports.

The CSS IDs must have been defined in the PART or PARTITION keyword on the RESOURCE statement. You can specify as many CSSs as you defined. If only a single CSS was defined, the CSS parameter is optional.

chpid
Specifies the channel paths in each CSS that are attached to the control unit. You must specify two hexadecimal digits for each channel path identifier (chpid) or two asterisks (**). You cannot duplicate chpid numbers within a CSS.
You can specify a maximum of eight chpids in a CSS. However, you can specify only one channel path in a CSS for:
  • An ESCON CTC control unit
  • A FICON CTC control unit
  • A control unit defined for FCP, IQD, OSC, OSD, OSE, OSM, OSN, or OSX channel paths (TYPE keyword).
You can specify a maximum of seven pairs of asterisks in a CSS. Each pair of asterisks specifies that a managed path (CHPARM keyword) can be added to the control unit and identifies the control unit as being managed by dynamic CHPID management. The number of pairs of asterisks specifies the number of managed paths that can be added to the control unit. The following restrictions apply to a managed control unit:
  • At least one chpid number must be specified in each CSS
  • You can specify a maximum of eight chpids and pairs of asterisks in a CSS
  • Only CNC, FCV, and FC channel paths (TYPE keyword) can be attached to the control unit
  • The channel paths attached to the control unit must be shared or spanned.

A spanned channel path is not required to attach to a control unit from each CSS to which the channel path is assigned.

The channel paths attaching to the control unit must be all unshared or all shared. You cannot mix shared and unshared channel paths to a control unit. All spanned channel paths are also shared channel paths.

You can assign a CNC, CTC, or FC channel path (TYPE keyword) to only one control unit unless one of the following statements is true:

  • The channel path is assigned to an ESCON or FICON Director (SWITCH keyword)
  • The control unit has a logical address (CUADD keyword).

You can assign a CFS, CFP, CBS, CBP, ICP, CIB, CL5, and CS5 channel path (TYPE keyword) to only one control unit. You cannot assign a CFR or CBR channel path (TYPE keyword) to a control unit. CFR and CBR channel paths do not require control units or devices.

You can assign an OSC, OSE, OSN, or FCP channel path (TYPE keyword) to only one control unit.

You can assign an IQD, OSD, OSM, or OSX channel path (TYPE keyword) to only one control unit unless the control unit has a logical address (CUADD keyword). If you need to define more than 256 devices for an IQD channel path or 254 devices for an OSD, OSM, or OSX channel path, define multiple control units. Specify a unique logical address for each control unit using the CUADD keyword.

All channel path types (TYPE keyword) attaching to a control unit must meet the following restrictions:
  • All CBY or CVC
  • All CNC, FCV, or FC
  • CTC
  • All CFS or CBS
  • All CFP, CBP, ICP, CIB, CL5, or CS5
  • OSC
  • OSD
  • OSE
  • OSM
  • OSN
  • OSX
  • FCP
  • IQD

You can intermix FC channel paths with CNC and FCV channel paths. To ease migrating from ESCON channels to FICON channels using dynamic I/O configuration, mix FC channel paths with CNC and FCV channel paths. The mixture allows you to dynamically add FC channel paths to a control unit while keeping its devices operational. A second dynamic I/O configuration change can then remove the CNC and FCV channels while keeping the devices operational.

For some types of control units and devices, there might be small operational performance differences when intermixing (for example, Resource Measurement Facility (RMF) usage calculations and channel path reconnection). Dynamic CHPID management cannot manage a control unit that contains intermixing. For these control units and devices, mixing of FC channel paths with CNC and FCV channel paths should be temporary. Non-dynamic I/O users are recommended to avoid mixing these channel paths.

When mixing ICP, CIB, CL5, and CS5 channel paths in the same control unit, the CSYSTEM keyword value on the CIB, CL5, and CS5 (if specified) channel paths must be identical to the local system name of the CPC (LSYSTEM keyword). When mixing CIB, CL5, and CS5 channel paths in the same control unit, any CSYSTEM keyword values that are specified for the channel paths must be identical. If a CS5 or CL5 channel path did not specify a CSYSTEM keyword value, it is ignored.

Other types of control units and devices fully support this intermixing. To determine the level to which your control units and devices support intermixing, see their device planning manuals. For control units that support intermixing, consult their performance white papers for guidance on how to best configure channels from a performance perspective. To improve the balance of workload across channels in an intermixed environment, alternate ESCON (CNC and FCV) and FICON (FC) channel paths in the control unit header for this control unit. Use the following patterns:

  • For 6 ESCON and 2 FICON, use a sequence of E, E, E, F, E, E, E, F
  • For 4 ESCON and 4 FICON, use a sequence of E, F, E, F, E, F, E, F
  • For 2 ESCON and 6 FICON, use a sequence of E, F, F, F, E, F, F, F.
LINK=
cssid
Specifies the logical channel subsystem (CSS) IDs associated with this parameter. A CSS ID is a 1-digit number in the range 0-n. See Table 2 to determine the maximum CSS ID your CPC supports.

Each CSS ID must have been specified in the PATH keyword for this control unit. You can specify as many CSSs as you specified in the PATH keyword. If only a single CSS was specified in the PATH keyword, the CSS parameter is optional.

link address
Specifies the link addresses to which the control unit is attached. The order in which the link addresses are specified for each CSS corresponds to the order in which the channel paths are specified in the CSS parameters of the PATH keyword. For example, the second link address identified for CSS 1 in the LINK keyword corresponds to the second channel path identified for CSS 1 in the PATH keyword.

The LINK keyword is optional if none of the channel paths in the PATH keyword attach to an ESCON or FICON Director (SWITCH keyword). You do not need to specify link addresses for a CSS if none of the channel paths specified for the same CSS ID in the PATH keyword attaches to an ESCON or FICON Director. You can specify two or four asterisks for link addresses that correspond to channel paths not attached to a director. For ESCON channel paths not attached to a director, specify any valid link address values.

FC channel paths not attaching to a director can specify only link addresses of asterisks. A link address of asterisks must be specified for each channel path in the PATH keyword that is specified as two asterisks (**). This pairing of asterisks in the PATH and LINK keywords of the CNTLUNIT statement indicates the number of managed paths (CHPARM keyword) that can be added to the control unit.

You must specify link addresses with two or four hexadecimal digits. The valid link address range is 01-FE for CBY, CVC, CNC, CTC, and FCV channel paths (TYPE keyword). The valid link address range is 0000-FFFF for an FC channel path. To determine whether to specify a 2- or 4-digit link address for an FC channel path and how to select a 4-digit link address, see Defining FICON switch configurations. When you specify a 4-digit link address for an FC channel path, every link address for that channel path must also be four digits.

If you specify the LINK keyword for a CSS, you must specify either a valid link address or asterisks for every channel path in the same CSS in the PATH keyword. If you do not specify the LINK keyword or specify asterisks, IOCP assumes that the link address is arbitrary and assigns a link address of 0D. Link addresses specified in the LINK keyword for dynamic connections through a director must equal the link addresses associated with the physical ports on the director to which the control unit is attached. However, link addresses specified for channel paths having dedicated connections through an ESCON Director can be arbitrary.

For channel paths having dedicated connections through an ESCON Director, specify the corresponding link address on the CNTLUNIT statement as the link address associated with the physical port on the ESCON Director to which the control unit is attached. If a CTC channel path does not attach to an ESCON Director or has a dedicated connection through an ESCON Director, the link address specified here might not be the link address the CSS uses.

For maximum availability of a control unit and its devices, see List of I/O devices and control units for recommendations for selecting the physical ports on an ESCON Director to attach to the control unit.

The LINK keyword is valid only for CBY, CVC, CNC, CTC, FCV, and FC channel paths (TYPE keyword).

Even though you can specify multiple link addresses for CBY and CVC channel paths (TYPE keyword), the I/O subsystem does not support dynamic connections through an ESCON Director for CBY or CVC channel paths. A CBY or CVC channel path that attaches to an ESCON Director can have only a dedicated connection through it. Therefore, you can connect only one link address on an ESCON Director to a CBY or CVC channel path at a time.

Note: If you specify no link address for a channel path that does not attach to a director, IOCP selects a link address of 0D to address the control units on the channel path. This arbitrary link address is displayed by the I/O Problem Determination (IOPD) frame and the IOCDS Display frame on the Support Element. However, the IOCP reports show that no link address was specified on its CNTLUNIT statements.
The I/O subsystem flags a channel path with a definition error in the following situations:
  • The channel path does not attach to an ESCON or FICON Director or has a dedicated connection through an ESCON Director and has more than one link address specified on its CNTLUNIT statements.
  • The channel path has a dynamic connection through a director and no link address was specified on the CNTLUNIT statement.
  • The channel path has 4-digit link addresses but is not connected to a high integrity fabric of FICON switches. For more information about high integrity fabrics, see Defining FICON switch configurations.

In these three instances, the channel path is unavailable and remains so until the error is resolved.

In addition to the preceding syntax rules, the following configuration rules also apply when specifying link addresses. For link addresses with four digits, rules are enforced against the switch to which the channel path is connected (that is, the entry switch) rather than the switch to which the control unit is attached. When a 4-digit link address is specified for a channel path, specify four-digit link addresses for all paths that have the same entry switch. Otherwise, IOCP cannot enforce some of the following switch configuration rules.
  • Specifying more than one link address for an ESCON channel path is not allowed unless the channel path is connected to an ESCON Director. Specifying any link address other than asterisks for an FC channel path is not allowed unless the channel path is connected to a FICON Director.
  • All channel path types (TYPE keyword) assigned to a link address on an ESCON Director must be identical, with the following exceptions:
    • CBY or CVC channel paths
    • CNC or FCV channel paths.
    These channel paths are the only ones you can assign to the same link address on an ESCON Director.
  • Specification of any given path (pchid.link) on more than one control unit is not allowed unless one of the following statements is true:
    • The control units attach to CBY or CVC channel paths (TYPE keyword).
    • The control units have unique logical addresses (CUADD keyword). See Example 6 for CNTLUNIT definition considerations.
  • The specification of FICON CTC and non-FICON CTC control units (see IOCP definitions) to the same link address on the same director is not allowed. The control units must either all specify UNIT=FCTC or none of them can specify FCTC.
  • The specification of multiple control units to the same link address on the same director is not allowed unless one of the following conditions is true:
    • The control units attach to CBY or CVC channel paths (TYPE keyword).
    • The control units are ESCON CTC or FICON CTC control units. (See IOCP definitions.) The path (pchid.link.cuadd) attaching to each control unit is unique. That is, the pchid, link address, or logical address (CUADD keyword) for the control unit must be different on each control unit.
    • The control units have the same unit address ranges and none of the paths attaching to the different control units belongs to the same logical partition. The logical partition intersection test is based on the initial access lists of the channel paths attaching to the control units.
    • Unique logical addresses (CUADD keyword) were specified on all the CNTLUNIT statements.
FC control unit definition considerations:
FC channel paths (TYPE keyword) support a maximum number of unit address ranges and unit addresses. (See Table 1.) IOCP calculates the number of unit address ranges and unit addresses for a spanned FC channel path (PATH keyword in the CHPID statement) as follows:
  • If a single link address is used for the channel path in each CSS of a control unit, one unit address range is counted and the number of unit addresses specified with the UNITADD keyword on the CNTLUNIT statement are counted once.
  • If different link addresses are used for the channel path in any of the CSSs of a control unit, one unit address range is counted for each unique link address and the number of unit addresses specified with the UNITADD keyword on the CNTLUNIT statement are counted once for each unique link address.

For example, CHPID 10 is an FC channel path that is spanned to CSSs 0, 1, 2, and 3. It is assigned to a control unit in CSSs 0, 1, and 3. The channel path uses link address C0 in CSSs 0 and 1 and link address D0 in CSS 3. Because there are a total of two unique link addresses, two unit address ranges are counted. If the UNITADD keyword specified 128 unit addresses, a total of 256 unit addresses are counted.

CUADD=address
Specifies the logical address for the control unit.

For example, the IBM Enterprise Storage Server® (ESS) 2105 control unit requires that the logical address specified with the CUADD keyword matches the control unit image address associated with the corresponding control unit logical subsystem (LSS).

Note: Not all ESCON and FICON control units support logical addressing.
The address is 1-2 hexadecimal digits in the range 0-F for CNC, CTC, and FCV channel paths and in the range 00-FF for FC, IQD, OSD, OSM, and OSX channel paths. However, if FC channel paths are mixed with CNC or FCV channel paths, the address must be in the range 0-F. The address allows you to specify a CNC, CTC, FCV, or FC channel path on multiple CNTLUNIT statements for a given path (pchid.link or switch.link) or to specify an IQD, OSD, OSM, or OSX channel path on multiple CNTLUNIT statements.
  • For CNC, CTC, and FCV channel paths, you can specify a maximum of 16 CNTLUNIT statements to specify the same pchid or the same link address for a pchid on an ESCON Director.
  • For FC channel paths, you can specify a maximum of 256 CNTLUNIT statements to specify the same pchid or the same link address for a pchid on a FICON Director.
  • For an IQD channel path, you can specify a maximum of 64 CNTLUNIT statements.
  • For an OSD, OSM, or OSX channel path, you can specify a maximum of 16 CNTLUNIT statements. The OSAD device with unit address FE requires a control unit definition with a CUADD keyword value of zero or no CUADD keyword. Otherwise, the device is unusable.
Note: A CNC or CTC channel path not assigned to an ESCON Director is viewed as having a single link address.

The CUADD keyword is valid only for: CNC, CTC, FCV, FC, IQD, OSD, OSM, and OSX channel paths (TYPE keyword).

For a channel path assigned to an ESCON CTC or FICON CTC control unit, the logical address identifies the logical partition to which this channel path is to communicate. If the remote channel path to which this channel path must communicate is not shared, then the logical address must be zero or not specified. If the remote channel path to which this channel path must communicate is shared, then the logical address must equal the wanted MIF image ID1 from the RESOURCE statement for the logical partition that the shared channel path can access. This applies to CNC, CTC, FCV, and FC remote channel paths that are shared.

However, if the remote channel path is a shared FC channel path on a CPC that supports multiple logical channel subsystems (that is, if the IOCP described in this document supports the CPC), then the logical address must equal the combination of the wanted CSS ID and the MIF image ID for the logical partition with which you want to communicate. For example, if the remote channel path is shared within CSS 1 and you want to communicate with the logical partition that has MIF image ID 5, specify CUADD=15.

ESCON CTC and FICON CTC communications are on a logical partition basis even if a channel path is shared by multiple logical partitions. You must define a control unit for every logical partition to which you want to communicate.

Note: The preceding CTC requirements for the CUADD keyword apply to any type of remote CPC (for example, a 9672 CPC).

For more information about ESCON CTC and FICON CTC communication, see ESCON and FICON Channel-to-Channel Reference, SB10-7034.

In addition to the preceding syntax rules, the following configuration rules also apply when specifying the CUADD keyword:
  • All CUADD values must be unique for a given path (pchid.link) regardless of whether a director was specified. That is, the combination pchid.link.cuadd is allowed only once in the configuration. SeeExample 6 for CNTLUNIT definition considerations.
  • For an IQD, OSD, OSM, or OSX channel path, you cannot duplicate CUADD values. Every control unit on the channel path must specify a unique CUADD value.
  • If the CUADD keyword is specified, the CUADD keyword must also be specified on all other CNTLUNIT statements that have at least one path in common (same switch.link or pchid.link).
  • If a channel path does not attach to a director (SWITCH keyword), specifying FICON CTC and non-FICON CTC control units on the same channel path is not allowed. See IOCP definitions. The control units must either all specify UNIT=FCTC or none of them can specify FCTC.
  • All CUADD values must be unique for a given path through a director (switch.link) unless the following conditions are true:
    • The control units are ESCON CTC or FICON CTC control units (see IOCP definitions), and the channel paths for each control unit are all the same type or a mixture of CNC and FCV.
    • The control units have the same unit address range. The channel paths in each control unit are all the same type or a mix of CNC and FCV, and none of the paths attaching to the different control units belongs to the same logical partition. The logical partition intersection test is based on the initial access lists of the channel paths attaching to the control units.

Otherwise, the combination switch.link.cuadd is allowed only once in the configuration.

PROTOCL=
Specifies the interface protocol that the parallel control unit uses when operating with the channel paths specified in the PATH parameter. The PROTOCL keyword is meaningful only for CVC channel paths (TYPE keyword). IOCP ignores the PROTOCL keyword for all other channel path types. IOCP assigns PROTOCL=D to control units attached to CBY channel paths.
Note: Incorrect specification of the PROTOCL parameter might produce unpredictable results. For example, if you specify PROTOCL=S (data streaming) for a control unit that supports the DC interlock protocol, I/O requests can result in detected errors (such as data overruns or interface control checks) or in undetected errors. Additionally, specifying PROTOCL=S for a control unit that runs at a maximum data rate of 4.5 MB per second could cause bus parity checks.
D
Specifies the direct-coupled interlock (DC interlock) protocol. This protocol is the standard I/O interface that requires a response to a demand. If you do not code PROTOCL, D is the default.
S
Specifies data streaming protocol at a maximum data rate of 3.0 mps (megabytes per second). This protocol does not require the demand response but continues at the rate governed by the control unit.
S4
Specifies data streaming protocol at a maximum data rate of 4.5 mps. This protocol does not require the demand response but continues at the rate governed by the control unit.
SHARED=
Specifies the level of concurrency of I/O requests that the parallel channel path allows for the control unit. IOCP automatically sets the control unit type (1 or 2) based on the SHARED parameter that you specify. See List of I/O devices and control units for more information about specifying the SHARED parameter. (For further information about control unit types, see Control unit types.)

The SHARED keyword is meaningful only for CVC channel paths (TYPE keyword). IOCP ignores the SHARED keyword for all other channel path types. Control units that attach to CBY, CNC, CTC, FCV, FC, FCP, IQD, OSC, OSD, OSE, OSM, OSN, or OSX channel paths are type 2. Control units that attach to CFS, CFP, CBS, CBP, CIB, CL5, CS5, and ICP channel paths are type 1.

Y
Specifies that the control unit supports:
  • Only one I/O request at a time, regardless of the number of I/O devices attached (for example, the 3803 Tape Control Unit for magnetic tape units or the 3258, 3272, or 3274 Control Unit)
  • Disconnect command chaining (DCC) operations.

IOCP assigns the control unit as type 1.

The channel ensures that only one I/O request is processed at a time for all devices sharing the control unit. If sense information is pending in the control unit for an I/O device attached to the control unit, the channel ensures that I/O requests for other I/O devices attached to the control unit are not initiated until the system control program has issued an I/O request to clear the pending sense information.

N
Specifies that the control unit supports multiple I/O requests concurrently (one for each attached I/O device). IOCP assigns the control unit as type 2. Specifying SHARED=N for a control unit that does not support multiple concurrent requests can result in a control unit malfunction.
UNIT=type
Specifies the type of control unit. You can specify as many as eight alphanumeric or special (-, #, @, or $) characters that identify the type of control unit. IOCP checks the syntax for alphanumeric or special characters.

IOCP takes special actions for control unit types SCTC and FCTC. See the LINK and CUADD keyword sections for the CNTLUNIT statement. Also, control unit type FCTC is valid only for FC channel paths (TYPE keyword).

You must specify a type for every control unit in your I/O configuration.

A Server Time Protocol (UNIT=STP) control unit with CIB, CL5, or CS5 channel paths (TYPE keyword) must have only external connections. No CIB, CL5, or CS5 channel path in an STP control unit can have a CSYSTEM keyword value that matches the local system name (LSYSTEM keyword) of the CPC, forming an internal connection. Also, an STP control unit cannot have ICP channel paths.

Notes:
  1. To define a FICON channel-to-channel (CTC) connection between FC channel paths (TYPE keyword), specify UNIT=FCTC for each CTC control unit defined on the FC channel path.
  2. For integrated control unit/devices (such as the IBM 3800 Page Printer), specify the same type value in the UNIT parameter of the CNTLUNIT statement as in the UNIT parameter of the IODEVICE statement. For example, for the IBM 3800 Page Printer, specify UNIT=3800 in each of the two statements.
UNITADD=
address
Specifies the unit addresses of the I/O devices that the control unit recognizes. You specify two hexadecimal digits in the range of 00-FF. For example, UNITADD=((0A),(0B),(0F)) specifies that the control unit recognizes unit addresses 0A, 0B, and 0F. At least one unit address must be specified. A unit address does not need to represent an attached device.
number
Specifies the number of sequential unit addresses the control unit recognizes. You specify a 1-, 2-, or 3-digit decimal value in the range of 1-256. For example, UNITADD=((0A,3)) indicates that the control unit recognizes unit addresses 0A, 0B, and 0C. The unit address plus the number of addresses must not exceed an address of FF. If the number is omitted, a value of 1 is assumed.
You can specify a maximum of eight addresses or sets of address and number values for parallel control units. For ESCON or FICON control units, you can specify only one range of unit addresses. The unit addresses specified for the CNTLUNIT statement must include the unit addresses of the attached devices. The unit address of a device is taken from the UNITADD parameter of the IODEVICE statement if specified or from the rightmost two digits of the device number specified with the ADDRESS parameter of the IODEVICE statement.
Note: See List of I/O devices and control units for some exceptions and recommendations that apply to specific device types. Some ESCON and FICON control units require unit address range to begin with (hexadecimal) 00.

IOCP ignores the UNITADD keyword for control units attached to CFS, CFP, CBS, CBP, CIB, CL5, CS5, FCP, ICP, IQD, OSC, OSD, OSE, OSM, OSN, or OSX channel paths. IOCP defines unit addresses 00-FE for control units attached to OSD, OSE, OSM, OSN, or OSX channel paths. IOCP defines unit addresses 00-FD for control units attached to FCP or OSC channel paths. IOCP defines unit addresses 00-FF for control units attached to IQD channel paths.

The full range of unit addresses that the control unit can address must be specified regardless of whether devices are attached. If you do not specify one or more of the unit addresses that the control unit can address, missing interruption handler (MIH) situations result. However, this requirement does not apply to ESCON CTC or FICON CTC control units.
Notes:
  1. Specify identical unit addresses in the CNTLUNIT statements for TYPE=CTC and TYPE=CNC or TYPE=FCV channel paths to communicate with each other. Specify identical unit addresses for FICON CTC control units to communicate with each other.
  2. Unit addresses must be unique for each chpid on parallel control units. Two control units attached to the same parallel channel path must have unique unit address ranges.
  3. Unit addresses must be unique for each control unit (not for each chpid) for ESCON, FICON, IQD, OSD, OSM, and OSX devices. Two devices attached to the same ESCON, FICON, FC, IQD, OSD, OSM, or OSX control unit cannot have the same unit address. However, two devices attached to the same CNC, CTC, FC, FCV, IQD, OSD, OSM, or OSX channel path (TYPE keyword) can have the same unit address if they attach to different control units.

A shared CTC channel path (SHARED keyword specified in the CHPID statement) can generate more unit addresses and unit address ranges than an unshared channel path. See Shared ESCON CTC considerations.

A spanned FC channel path (PATH keyword in the CHPID statement) can generate more unit addresses and unit address ranges than an unspanned channel path. See "FC control unit definition considerations" on page FC control unit definition considerations:.

1 For IOCP programs not described by this document, the MIF image ID was called a partition number.