HP 3000 Manuals HP 3000 Manuals
IBM 3270 Differences and Limitations
Certain limitations restrict VPLUS forms design or modification for IBM
3270 display stations. The following information explains how an IBM
3270 differs from an HP 3000 terminal and the impact of these differences
when running VPLUS applications using SNA DHCF/XL.
Keyboard Differences
Table 1-1 compares HP 3000 terminal keys with equivalent IBM 3270 keys.
Table 1-1. Comparison of Major Keys
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| | |
| HP 3000 Key | Equivalent IBM 3270 Key and Explanation |
| | |
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| | |
| AIDS | No equivalent key exists. |
| | |
| BREAK | PA1 - Equivalent to a system break. |
| | |
| CLEAR DISPLAY | CLEAR - Clears the entire screen, including data and the form itself. |
| | The equivalent HP key only clears the data fields. Consequently, |
| | special built-in support handles this key as a special function key. |
| | SNA DHCF/XL transmits this key, and the VREADFIELDS intrinsic |
| | initiates a $REFRESH and reads again. |
| | |
| CLEAR LINE | ERASE EOF - Clears data in an unprotected field from the cursor to the |
| | end of the field, regardless of the number of lines in the field. |
| | This differs slightly from CLEAR LINE, which performs the same |
| | function only if the field does not exceed one line. |
| | |
| CTRL | No equivalent key exists. |
| | |
| CTRL y | PA2 - Equivalent to a subsystem break. Because VPLUS disables this |
| | key, SNA DHCF/XL ignores the key when pressed and reenables the |
| | keyboard. |
| | |
| DEL LINE | No equivalent key exists. |
| | |
| ENTER | ENTER - Locks the keyboard and transmits all modified data. The |
| | cursor remains in the same position. |
| | |
| ESC | No equivalent key exists. |
| | |
| INS LINE | No equivalent key exists. |
| | |
| MODES | No equivalent key exists. |
| | |
| NEXT PAGE | No equivalent key exists. |
| | |
| PREV PAGE | No equivalent key exists. |
| | |
| RESET | RESET - Unlocks a locked keyboard. |
| | |
| ROLL DOWN | No equivalent key exists. |
| | |
| ROLL UP | No equivalent key exists. |
| | |
| USER KEYS | No equivalent key exists. |
| | |
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In addition to the keys listed above, IBM 3270 program function keys
differ from HP 3000 function keys. The IBM keyboard has 12 or 24 program
function keys; the first eight of these keys map to the eight function
keys on HP keyboards.
Table 1-2 shows the mapping of IBM 3270 keys to HP keys. Note that the
Lastkey Value column refers to the Lastkey value in the COMAREA, which
VREADFIELDS sets after the user presses a function key or ENTER. When a
user presses an IBM key, a value passes to Lastkey, which is mapped to
the corresponding HP key. For instance, when an IBM user presses PF1,
VREADFIELDS returns the value of 1 to Lastkey. VREADFIELDS would return
the same value if an HP terminal user pressed HP function key F1.
Table 1-2. Mapping of Keys
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| | | |
| IBM 3270 Keys | HP Keys | Lastkey Value |
| | | |
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| | | |
| PF1, PF13 | F1 | 1 |
| | | |
| PF2, PF14 | F2 | 2 |
| | | |
| PF3, PF15 | F3 | 3 |
| | | |
| PF4, PF16 | F4 | 4 |
| | | |
| PF5, PF17 | F5 | 5 |
| | | |
| PF6, PF18 | F6 | 6 |
| | | |
| PF7, PF19 | F7 | 7 |
| | | |
| PF8, PF20 | F8 | 8 |
| | | |
| ENTER | ENTER | 0 |
| | | |
| PF9, PF21 | ENTER | 0 |
| | | |
| PF10, PF22 | ENTER | 0 |
| | | |
| PF11, PF23 | ENTER | 0 |
| | | |
| PF12, PF24 | ENTER | 0 |
| | | |
| PA1 | BREAK | |
| | | |
| PA2 | CTRL Y | |
| | | |
| CLEAR | None (Refresh function) | |
| | | |
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Screen Differences
SNA DHCF/XL affects the screen design of VPLUS applications for IBM 3270
display stations in the following areas:
* Screen attributes.
* Screen enhancements.
* Function key labels.
* Fields.
* Character translation.
Screen Attributes. IBM 3270 display stations have the following screen
attributes and limitations:
Display Area Depending on the IBM 3270 display station model, the
display area is either 24, 32, or 43 lines long. VPLUS
only allows you to compile forms for the IBM 3270 that can
fit within the smallest display area, which is 24 lines.
If the number of lines in a form exceeds 24, the compiler
displays an error message indicating that the form has too
many lines.
VPLUS reserves the last two lines of the display area for
function key labels. Therefore, a form can consist of
either 21 lines including a window line, or 22 lines
without the window line.
Status Line A status line appears below the display area. SNA DHCF/XL
applications, including VPLUS, cannot access the status
line. Only the display controller can update this line.
VPLUS Window A window line defined in a forms file occupies a line of
Line the available display. If you define a window line in the
forms file, you must place the window line on line 1 or
line 22, because IBM 3270 limitations prohibit inserting a
line in the middle of a form. Selecting a window line
reduces the maximum form length to 21 lines.
SNA DHCF/XL limits the text in a window line to 79 bytes
instead of 80, because space must be reserved for the
attribute byte. Text exceeding 79 bytes becomes truncated.
(Refer to the section "Fields" for information about the
attribute byte.)
Modified An IBM 3270 functions as a modified data tag (MDT) device.
Data Tag It transmits to the HP 3000 only the data that the end user
has modified.
Limitations The following IBM 3270 limitations are important to note
when designing or modifying VPLUS applications. Unlike HP
terminals, the IBM 3270 does not have:
* Forms caching capability.
* Terminal memory other than display memory, which
consists of a 24-line length and 80-column width.
* Scrolling capability.
In addition, the IBM 3270 does not support:
* The line-drawing character set provided on some HP
terminals.
* Local field edits that occur in the terminal firmware,
such as edits for numeric fields.
Screen Enhancements. Several HP terminal display enhancements are not
available on the IBM 3270. You do not have to alter any enhancements
specified in an existing forms file for IBM 3270 usage, because HP
display enhancements map to non-display, normal display, or intensified
display on IBM 3270 display stations.
HP display enhancements map to IBM 3270 display stations as follows:
* If one or more characters of an HP display enhancement code contain
the letter H, but not the letter S, this maps to a normal display for
the IBM 3270.
* If one or more characters of an HP display enhancement code contain
the letter S, this maps to a non-display for the IBM 3270.
* If one or more characters of an HP display enhancement code contain
any characters other than S or H, this maps to an intensified display
for the IBM 3270. All color pairs also map to an intensified display
for the IBM 3270.
Function Key Labels. VPLUS simulates function key labels by reserving
the last two lines of the screen. This reduces the available screen area
to 22 lines.
Function key labels for IBM 3270 display stations appear similar to those
for HP terminals. The label text appears on an IBM 3270 display station
as intensified display on a blank background. If function key labels are
not used in the application, default function key labels are simulated.
Fields. You should not design a form that has contiguous fields, because
the IBM 3270 display station requires an attribute byte preceding each
field or text area. The attribute byte uses a physical screen location
and appears as a blank space on the screen. The attribute byte indicates
whether the field can be or has been changed.
You can create a space for both leading and trailing attribute bytes by
inserting visible brackets before and after all fields. FORMSPEC
converts these visible brackets to invisible attribute bytes on IBM
3270s. The following example shows how you could define three fields
using visible brackets and how they would appear when the VPLUS form is
displayed on an IBM 3270 screen.
[08][05][52]
08 05 52
If you use invisible brackets to delimit fields, you must provide a
leading space before each field or text area. When the field or text
begins in the first column of a line, insert the space at the end of the
previous line. The "Home" position is an exception to this guideline;
the attribute byte is inserted in the bottom right corner instead
(reverse "Home").
Character Translation. HP computer systems use the ASCII character set
and IBM computer systems use the EBCDIC character set. Consequently, SNA
DHCF/XL must use system default translation tables from Native Language
Support (NLS) to translate characters from one system to the other.
If Native-3000 is the language used, SNA DHCF/XL translates all ASCII
characters without alterations, except for the characters shown in Table
1-3. Note that the HP terminal bracket characters equate to text, not
actual FORMSPEC brackets.
Table 1-3. Differences Between HP and IBM Character Displays
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| | | | |
| HP Terminal | ASCII | IBM 3270 | EBCDIC |
| Character | Hex Value | Character | Hex Value |
| | | | |
-------------------------------------------------------------------------------------------------
| | | | |
| [ | 5B | В | 4A |
| | | | |
| ] | 5D | ! | 5A |
| | | | |
| ! | 21 | | | 4F |
| | | | |
| ^ | 5E | - | 5F |
| | | | |
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To display one of these characters on one system, you must specify the
corresponding character on the other system. For instance, if you want
to send a vertical bar (|) to an IBM 3270 user, your VPLUS application
must specify this character as an exclamation point (!).