The Read a Single Character routine reads a keystroke and returns
    that keystroke's terminator code.

    Format

      SMG$READ_KEYSTROKE  keyboard-id ,word-terminator-code

                          [,prompt-string] [,timeout] [,display-id]

                          [,rendition-set] [,rendition-complement]

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

2  –  Arguments

 keyboard-id

    OpenVMS usage:identifier
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Keyboard identifier. The keyboard-id argument is an unsigned
    longword containing the identifier of the virtual keyboard from
    which to read.

    You can create a virtual keyboard by calling the SMG$CREATE_
    VIRTUAL_KEYBOARD routine.

 word-terminator-code

    OpenVMS usage:word_unsigned
    type:         word (unsigned)
    access:       write only
    mechanism:    by reference

    Key terminator code. The word-terminator-code argument is an
    unsigned word into which is written a code indicating what
    character or key terminated the read. Key terminator codes are
    of the form SMG$K_TRM_keyname.

 prompt-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    Prompt string. The prompt-string argument is an optional string
    used as the prompt for the read operation.

 timeout

    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       read only
    mechanism:    by reference

    Timeout count. The timeout argument is optional. If specified,
    any character typed before the timeout is returned in the buffer.

 display-id

    OpenVMS usage:identifier
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Display identifier. The optional display-id argument is the
    address of an unsigned longword that contains the identifier
    of the virtual display in which the read is to be performed.
    If the optional prompt-string argument is specified while there
    are multiple virtual displays pasted, the display-id argument is
    required to determine in which virtual display the prompt string
    will be written. If the prompt-string argument is not specified,
    do not specify the display-id argument.

    In the case of multiple virtual displays, each virtual display
    has an associated virtual cursor position. At the same time,
    there is a single physical cursor position corresponding to
    the current location of the physical cursor. If the display-id
    argument is specified, the read begins at the current virtual
    cursor position in the specified virtual display. If display-
    id is omitted, the read begins in the current physical cursor
    position. Note that the length of the prompt-string plus the
    key entered is limited to the number of visible columns in the
    display.

 rendition-set

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Attribute specifier. The optional rendition-set argument is
    the address of a longword bit mask in which each attribute set
    causes the corresponding attribute to be set in the display. The
    following attributes can be specified using the rendition-set
    argument:

    SMG$M_BLINK     Displays blinking characters.
    SMG$M_BOLD      Displays characters in higher-than-normal
                    intensity.
    SMG$M_REVERSE   Displays characters in reverse video; that is,
                    using the opposite of the default rendition of
                    the virtual display.
    SMG$M_          Displays underlined characters.
    UNDERLINE
    SMG$M_USER1     Displays user-defined attributes.
    through
    SMG$M_USER8

    The display-id argument must be specified when you use the
    rendition-set argument.

 rendition-complement

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Attribute complement specifier. The optional rendition-
    complement argument is the address of a longword bit mask in
    which each attribute set causes the corresponding attribute to
    be complemented in the display. All of the attributes that can
    be specified with the rendition-set argument can be complemented
    with the rendition-complement argument. The display-id argument
    must be specified when you use the rendition-complement argument.

    The optional arguments rendition-set and rendition-complement
    let the user control the attributes of the virtual display. The
    rendition-set argument sets certain virtual display attributes,
    while rendition-complement complements these attributes. If the
    same bit is specified in both the rendition-set and rendition-
    complement parameters, rendition-set is evaluated first, followed
    by rendition-complement. By using these two parameters together,
    the user can control each virtual display attribute in a single
    procedure call. On a single-attribute basis, the user can cause
    the following transformations:

    Set  Complement Action

    0    0          Attribute set to default
    1    0          Attribute on
    0    1          Attribute set to complement of default setting
    1    1          Attribute off