HP 3000 Manuals HP 3000 Manuals
HP and IBM Terminal Characteristics
HP terminals and IBM 3278 display stations differ in some of their
characteristics and functionality. This section describes the
differences between HP and IBM terminals.
Non-Display Input Fields
On an IBM 3278 display station, you can enter data into a non-display
unprotected field, and the data does not appear on the screen. Although
HP terminals do not support non-display fields, SNA IMF has several ways
of implementing the non-display feature.
1. SNA IMF supports security video on the following HP terminals:
2624A 2624B 2620A 2626A
2392A 2392X 2394A 2397A
150A 700/92 700/94
Security video emulates the non-display feature of 3278 terminals.
Data that you type into a non-display field is retained in
terminal memory, but it is not displayed on the screen.
2. On terminals that do not support security video, SNA IMF/V
displays meaningless symbols from alternate character set C in
non-display fields.If your HP terminal does not have a character
set C, but it has an A or B character set, no symbols are
displayed and the terminal functions like a 3278 display station.
If your HP terminal does not have an alternate character set, but
has only the standard character set, the emulated IBM 3278
non-display feature is not available with SNA IMF/V; anything you
type in a non-display field is printed on the screen.
If you are using non-display input fields with a 264x terminal,
slot C must be empty.
Press the terminal TEST keyto determine whether your terminal has
an alternate character set. The resultant test pattern displays
any alternate character sets that are installed in your terminal.
3. On HP graphics terminals, data that you type into non-display
fields is printed black-on-black.
If the IBM host sends data to a non-display unprotected field, SNA IMF
does not send the data to an HP terminal. Anything you type into a
non-display field on an HP terminal replaces the original data from the
IBM host. An IBM 3278 changes only that part of the field in which data
has been entered. This can be a problem for some applications.
Cursor Addressing
When an IBM 3278 display station user presses the transmit key, the
current cursor addressis sent to the IBM host. If your HP terminal is
connected to the IBM host over a Datacommunications and Terminal
Controller (DTC), an Asynchronous Data Communications Controller (ADCC),
or an Asynchronous Terminal Processor (ATP), the current cursor address
is sent to the host when you press the transmit key.
For SNA IMF/V, HP terminals connected to the HP 3000 over a multipoint
line always send the cursor address as though the cursor were positioned
in the upper left corner of the screen; that is, buffer position (0,0).
This pseudo cursor address causes problems if the IBM host application is
expecting to receive the exact cursor address. For example, Pass Thru
cannot support the split screen mode of the IBM Structured Programming
Facility (SPF) on multipoint terminals.
Cursor Positioning
On an IBM 3278 display station, the IBM host can position the cursor
within a protected field after you enter the first character of input.
Pass Thru cannot place the cursor within a protected field. If the IBM
host attempts to position the cursor within a protected field, Pass Thru
positions the cursor at the start of the next unprotected field before
enabling input. This produces the same results as pressing the TAB keyas
the first character on an IBM 3278 display station.
If you type a character into the last position on the screen (the lower
right-hand corner), your HP terminal temporarily rolls the screen up one
line. If you type another character, the screen rolls back down to its
correct position. The cursor homes, and your character is placed
correctly in the first character position on the screen (the upper
left-hand corner). However, if you cause the screen to roll up, you must
home the cursor before you send the screen's data to the host. If you
attempt to send data while the screen is rolled up, you will receive an
error message, and no data will be sent to the host.
Unprotected Fields
Typing a character into an unprotected field of an IBM 3278 display
station sets the Modified Data Tag (MDT) for that field. Later, when you
press the transmit key, only the fields with the MDT set are sent to the
host.
Hewlett-Packard makes both MDT and non-MDT terminals. MDT terminals have
a Modified Data Tag associated with each field, just like IBM 3278
display stations. Non-MDT terminals do not support Modified Data Tags.
MDT and non-MDT terminals differ in the way they handle null and blank
characters.The HP 700/94 terminal now has a ROM module (part #5062-1306)
that allows it to support null characters, but all of the older HP
terminals represent null characters as blanks. For more information on
null character translation on MDT and non-MDT terminals, see "Leading
Blanks, Trailing Blanks, and Trailing Nulls," in chapter 2.
Unprotected Fields on HP MDT Terminals.
When you type a character into an unprotected field on an HP MDT
terminal, the terminal sets the Modified Data Tag for that field. Only
the fields with the MDT set are transmitted to the HP 3000 when you press
a transmit key. If you type identical data over the existing data in the
field, it is transmitted to the HP 3000.
Unprotected Fields on HP Non-MDT Terminals.
Striking a transmit key on an HP non-MDT terminal that is under Pass Thru
control causes the HP 3000 to read all unprotected fields in the screen.
Pass Thru then sets the Modified Data Tags for the unprotected fields.
Each unprotected field received from the terminal is compared with the
unprotected field last written to the terminal by Pass Thru. If the data
in a field has changed, the MDT is set for that field, and the field is
then sent to the IBM host. If you type identical data over the existing
data in a field, the HP 3000 compares it with the original data, finds no
difference, and does not transmit it to the IBM host.
Displayed Symbols
All characters written to an HP Pass Thru terminal by an IBM program must
correspond to ASCII characters (40 through 377 octal, or 20 through FF
hexadecimal). If they do not, the HP terminal cannot display them.
Certain characters displayed on an HP terminal will differ from those
displayed on an IBM display station. Table 5-5 summarizes these
differences.
Table 5-5. IBM to HP Character Display Differences
-----------------------------------------------------------------------------------------------
| |
| IBM Display EBCDIC Values HP Terminal ASCII Values |
| Station Character Character |
| |
| Octal Hex Octal Hex |
| |
| cents (cent sign) 112 4A [ (left bracket) 113 5B |
| (on IBM terminal) |
| |
| ! (exclamation) 132 5A ] (right bracket) 135 5D |
| |
| | (logical OR) 117 4F ! (exclamation) 041 21 |
| |
| NOT (not sign) 137 5F ^ (caret) 136 5E |
| |
-----------------------------------------------------------------------------------------------
NOTE IBM host programs should not send characters that equate either to
HP terminal escape sequencesor to control characters that perform
device-dependent functions on HP terminals.
Transmitted Printer Commands
The IBM host can send printer commandswithin a data stream to an IBM 3278
display station. New Line (NL), End of Message (EM), Carriage Return
(CR), and Form Feed (FF)are examples of printer commands. When the IBM
host transmits printer commands to an IBM display station, the display
station displays either a blank or a character (depending on the display
station model and the command sent). If the display station sends the
printer command back to the host within a modified field, the host
receives the correct code for the printer command.
If a printer command is sent to an HP terminal during a Pass Thru
session, SNA IMF saves the printer command in the internal screen image
and displays a character on the HP terminal screen. The character
displayed on the HP terminal may not be the same as the character
displayed on an IBM display station.
If you modify a field that contains a printer command, when SNA IMF
transmits that field to the host, it will transmit the character
representing the printer command, not the printer command itself.
You cannot enter a FIELD MARK (FM)in Pass Thru. If the host sends an FM,
Pass Thru displays it as a semicolon ( ; ). An IBM 3278 display station
also displays a semicolon for FM. However, if you send a semicolon within
a modified field back to the host, the host receives a semicolon instead
of the FM code.
Intensified Fields
Unlike IBM display stations, HP terminals cannot turn off inverse
videofor part of a field. The white stripe of inverse video extends the
full length of the field, even if the data does not fill the field.
Blinking Cursor
The cursor of an HP terminal always appears as a blinking underline. The
user of an IBM 3278 display station may choose to have the cursor appear
as a solid underline, a box, a blinking underline, or a blinking box.
Function Indicators
An IBM 3278 display station has a row of indicator symbols, including (1)
SYSTEM AVAILABLE, (2) INSERT MODE, and (3) INPUT INHIBITED, at the bottom
of the display station screen. This row of symbols is called the
operator information area. The HP indicator light associated with the
INSERT CHAR key is the only equivalent to the IBM operator information
area.
Numeric Fields
Unlike IBM terminals, HP terminals do not differentiate between numeric
fields and alphanumeric fields. Pass Thru treats numeric and
alphanumeric fields the same. Pass Thru does not provide a numeric-only
check in fields defined as numeric, so you are responsible for making
sure the data you enter in numeric fields is numeric data.
Field Manipulations
On an HP terminal, you should not do any explicit field manipulations,
such as FORMAT MODE ON, START FIELD, or STOP FIELD. Pass Thru does not
support such field manipulations.
Automatic Skip
An HP terminal's automatic skip feature does not function the same as the
IBM 3278 display station's automatic skip feature.
On an IBM display station, the automatic skip feature positions the
cursor at the next field. On an HP terminal, the automatic skip feature
positions the cursor at the next unprotected field.
Card Reader, Light Pen, and Cursor Select
An HP terminal does not have a magnetic card reader, auxiliary card
reader, light pen, or cursor select function.
Screen Sizes
The IBM host specifies the screen size of an HP terminal as 480, 1920, or
3440 characters. No other screen sizes can be emulated. IBM application
programs can use the ERASE/WRITE ALTERNATE commandof the IBM 3278 display
station to change screen sizes from 480, 1920, or 3440 characters (the
defaults) to 960, 2560, or 3564 characters. This feature does not work
on HP Pass Thru terminals. ERASE/WRITE ALTERNATE commands received from
the IBM host by SNA IMF are not supported; however, they are not
rejected. ERASE/WRITE ALTERNATE commands are mapped to ERASE WRITE
commands.