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Page of SH20-0634-1 Revised March 19, 1971 By TNL SN20-2339
MESSAGE FORMATS AND STRUCTURES
There are three basic message formats used within IMS/360:
• Input message
• Output message
• Program-to-program messages
The formats shown represent message segments as they would be
received or constructed in the segment I/O area. A message segment and a single message line are synonymous.
Input Message Format
Input message segments originate at a communications terminal and are delivered to the application program's segment I/O area by means of a GU or GN call to Data Language/I. An input message segment may be a
maximum of 131 bytes for the 1050 or 2740 terminals, including the count and the halfword reserved area. An input message segment may be a
maximum of 84 bytes for the 2260, including the count and halfword reserved area,. An input message from a 2260 may be a maximum of 959 characters (plus the SMI symbol). The format of each input message is:
r---,
I I I I
I LL I Z Z I TEXT I
I L _________________________________________________________ I I J I
where:
LL
ZZ
is a halfword binary field containing the total number of characters in the message line, including LL and ZZ. The value of LL
=
numberof characters in text + 4. This count entry is made by IMS/360 for input messages. When PL/I is used, this count is also placed in the dope vector's current length field segment I/O area. Further, with PL/I, the LL field is defined as a fullword but used as a halfword
(length of LL for total input message is two bytes). See the section titled ·segment Input/Output Areas· in Chapter 5 of this manual.
is a two-byte field whose value and use are reserved by IMS/360.
TEXT
is the message line exactly as i t was entered at the terminal in EBCDIC. The text includes transaction code, message text, and CR
(carriage return). If the message consists of multiple lines of text, each subsequent line has the same format. The message
consists of an unlimited number of segments. The transaction code appears only in the first line. If a password is entered with the message from the terminal, i t is edited out upon presentation to the application program, and the text is left-justified, as required. A transaction code must be followed by a blank or a left parenthesis i f there is a password. These are the only two acceptable
delimiters for the transaction code.
When the remote mode IBM 2260 Display station, Modell, is used as the input message device, the following are input message
considerations:
• The length of the message is variable from 1 to 960 characters.
• The input message is broken into segments. The segments will be either 80 characters in length or a length less than 80 characters if a new-line symbol is placed in the segment by the operator.
Maximum length of segments is 80 characters. (The Modell 2260 Display Station allows 80 characters horizontally and 12 lines vertically.)
• Therefore, the same Data Language/I rules apply to obtain each segment that makes up the input message.
• Only single screen input is allowed.
• The /EXCLUSIVE command should be used when entering an input message from a 2260 Display Station. If not, any BROADCAST or system
messages will be displayed on the screen and may erase an entry or an answer. When the /EXCLUSIVE command is used, the BROADCAST system messages will remain on the queue until an /END command is entered.
• WARNING: A START HI symbol must precede any entry of an input message. The operator of the 2260 can enter the START MI symbol from his keyboard, or the application program can place i t on the display screen. (If PL/I is used, the symbol must be one character multipunched, hexadecimal 4A.) Only one START MI symbol is allowed per screen.
• The input message for a 2260 is considered to be that data contained between the START HI symbol ( ) and the position of the CURSOR
symbol ( ) at the time the ENTER key is depressed. All other data displayed on the screen at this time is ignored and is not
transmitted to the cPU. If no START MI symbol is displayed at the time the ENTER key is depressed, no data is sent to the CPU.
• I t is recommended that, after a transaction is input, the operator should await his reply, i f one is expected, before entering another transaction. This will prevent the reply from one program from overlaying the reply from another before the operator has viewed i t . Output Message Format
output message segments or lines originate within the application program and are sent to a communications logical terminal, which is defined by a terminal PCB. Each output message segment is enqueued to be sent by means of an ISRT call to Data Language/I. The format of each segment is:
r---,
, I I ,. I
, L L I Zl I Z2 I TEXT I
, I " I
L ~
where:
LL
84
is a two-byte binary field containing the total number of characters in the message segment, including LL, Zl, and Z2. The value of LL
=
number of characters in text + 4. The application program must fill
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)
in this count. When PL/I is used, the LL field is defined as a binary fullword. The PL/I user must also place the length of the text to be written in this field. The values must represent the total of
/
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84.2
./ begin writing output segment at the position Indicates the screen will be erased. first; terminals. It is the application programmer's responsibility to
insert the required carriage-return character in the body of the message line segment. The length of an output message line segment must not exceed 960 characters of text for the 2260 Display station.
An output message can contain multiple segments. It is not necessary to include the logical terminal name in the output message, as the destination is determined by the PCB.
certain device control characters must be inserted into the message where desired to format the message at the terminal output device.
(In PL/I, these control characters must be initialized to one character and multipunched.) These are described below in hexadecimal format:
05: skip to tab stop, but stay on same line
15: start new line at left margin (carriage return)
25: skip to new line, but stay at same print position
When the remote mode IBM 2260 Display Station, Modell, is used as the output message device, the following are output message
considerations:
• An output message may be composed of multiple segments that make up a single display screen (12 lines times 80 characters equals 960 characters).
• Each output segment can have its own WRITE command. However, a WRITE ERASE (WE) will be ignored except on the first output segment.
• Only single screen output is allowed.
Examples of 2260 WRITE Commands
Example
!:
86
Segment 1:
has LL=9, Zl= binary zeros, Z2= hexadecimal 15, and
TEXT=ABCDE,. From the Z2 indication, this means erase screen and start writing at line 5.
Segment 2:
has LL=9, Zl and Z2= binary zeros, and TEXT=XYZ12. From the Z2 designation. this means continue writing TEXT from the last cursor position.
Segment 3:
has LL=ll, Zl= binary zeros, Z2= hexadecimal 08, and TEXT=QRSTUVW. From the Z2 indication, this means writing TEXT at line 8.
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1 2 3 4
SCREEN DISPLAY
r---5 ABCDEXYZ12
6 7
8 QRSTUVW
9 10 11 12
L ___________________________________ _
Example 2:
Segment 1:
has LL=ll, Zl= binary zeros, Z2= hexadecimal 20, and
TEXT=123456i. Z2 indicates that the screen shall be erased, and writing will start at the top left corner, ending the text with a new-line symbol.
Segment 2:
has LL=10, Zl=binary zeros, Z2= hexadecimal 20, and
TEXT=STUVWX. Z2 indicates that the screen should be erased and writing should start at the top left corner of the
screen, but, since there has already been a WRITE ERASE" this command will be ignored, putting the TEXT on the second line.
Segment 3:
has LL=9, Zl= binary zeros, Z2= hexadecimal 17, and
TEXT=XYZ99. Z2 indicates that the screen should be erased (WRITE ERASE) and TEXT placed on line 7. Since this is not the first segment command in this message, the WRITE ERASE will be ignored and the TEXT placed on line 7.
SCREEN DISPLAY
r---1 123456'
2 STUVWX
3 4 5 .6
7
XYZ998 10 ~
11 12
A 2260 application program done in PL/I is included as an example of a message program in the Appendix of this manual.