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3270 Host Connection Program 2.1 and 1.3.3 for AIX: Guide and Reference

HCON Display Emulation

HCON supports the emulation of a 3270 display session in Models 2, 3, 4, and 5. The display session can communicate with System/370 host processors using the 3270 data stream architecture. Some display models might not be available in certain ASCII displays.

The connection to a mainframe host can be:

The 3270 data stream architecture includes:

For a detailed description of data stream architecture, see the 3270 Information Display System Data Stream Programmer's Reference.

3270 Data Stream Attributes

The 3270 display session supports field attributes, extended field attributes, and character attributes.

Field Attributes

The bit assignments for field attributes supported by 3270 display sessions include:

EBCDIC Bit Field Description
0,1 Value determined by contents of bits 2-7.
2 0 = Unprotected 1 = Protected
3 0 = Alphanumeric 1 = Numeric* Note: Bits 2 and 3 set to 1 can cause an automatic skip.
4,5 00 = Display/not cursor-select-key detectable 01 = Display/cursor-select-key detectable 10 = Intensified display/cursor-select-key detectable 11 = Nondisplay, nonprint, nondetectable
6 Reserved
7 Modified Data Tag (MDT); identifies modified fields during Read Modified command operations. 0 = Field has not been modified. 1 = Field has been modified by the operator. Can also be set by program in data stream.
*Numeric field is not enforced. It is treated as an alphanumeric field.

Extended Field Attributes

These attribute types and attribute values are used in the Start Field Extended (SFE), Modify Field (MF), and Set Attribute (SA) orders.

Attribute Type Code SFE, MF Orders SA Orders
Character Attribute Reset X`00' - x
Field Attribute X`C0' x -
Extended Highlighting X`41' x x
Color X`42' x x
Programmed Symbols X`43' x x
Background Transparency X`46' x x
Note: Lowercase x indicates the type code is valid when used in the order.

Valid attribute values for each attribute type code.

Type Value Result
X`00' X`00' This is the only valid setting for this attribute type. All character attributes that can be specified in SA order are set to default value.
X`C0'
The codes appearing here have the same format as that of the field attribute codes preceded by the SF order.
X`41' X`00' X`F1' X`F2' X`F4' Default (Normal) Blink Reverse Video Underline
X`42' X`00' X`F1' X`F2' X`F3' X`F4' X`F5' X`F6' X`F7' Default (Green) Blue Red Pink Green Turquoise Yellow White
X`43' X`00' Default (Base Character Set)
X`46' X`FF' Non-Transparent

3270 Data Stream Commands

The 3270 data stream commands include:

Command Mnemonic Hex Line Code
write WR F1
erase/write EW F5
erase/write alternate EWA 7E
erase all unprotected EAU 6F
read modified RM F6
read modified all RMA 6E
read buffer RB F2
write structured field WSF F3

The definitions of the 3270 data stream commands are:

write (WR) Sends orders or data to update the display screen. Data characters are stored in successive buffer locations until an order is received in the data stream that alters the buffer address, or until all data has been received.
Note: The write command must be followed by a Write Control Character (WCC). A WCC Reset bit with the write command is not effective.

erase/write (EW)

erase/write alternate (EWA) Clears the screen before the write operation is started. The write operation starts from the buffer address 0.
Note: The erase/write command must be followed by a Write Control Character (WCC). If the WCC Reset bit is used, the Inbound Reply Mode is reset to Field.
erase all unprotected (EAU) Performs the following:
  • Clears all unprotected character locations and associated character attributes.
  • Resets the Modified Data Tag (MDT) bit in each unprotected field.
  • Unlocks the keyboard.
  • Resets the Attention Identifier (AID) to X`60'.
  • Repositions the cursor to the first character space in the first unprotected field.

If the screen is unformatted or contains only the protected field, the cursor will be repositioned to buffer address 0.

read modified (RM) Initiates one of five operations:
  • Read modified
  • Short read
  • Cursor select
  • Test request read
  • Inbound retry

When issuing the read modified command as unsolicited, the inbound transmission will be in a complete read modified format with an AID of X`60'. Issue the read modified command to try an inbound transmission again. If issued while the display is in a retry state, the read modified command causes the original inbound operation to repeat.

read modified all (RMA) Operates like the read modified command except both addresses and data from all modified fields are sent to the host, regardless of the AID byte generated. The read modified all command is available only in the SNA environment.
read buffer (RB) Causes all data in the display buffer to be transmitted inbound. The read buffer command is provided for diagnostic purposes.
write structured field (WSF) Enables the user to send one or more structured fields.

Write Control Characters

The Write Control Character (WCC) bits have these definitions.

WCC Bit Explanation
0 No function.
1 No function for the WR command. Reset function, if set to 1, for EW and EWA commands.
2, 3 Reserved.
4 Starts printer (SNA only). When set to 1, initiates a local-copy operation at the completion of the write operation.
5 Sounds alarm. When set to 1, causes the audible alarm to sound.
6 Restores keyboard. When set to 1, causes keyboard operation to be restored (by resetting system lock or WAIT indicator) and resets AID to X`60'.
7 Resets MDT bits in field attributes (WR command only). When set to 1, causes MDT bits to be reset to 0 in all field attribute bytes before any orders or data characters are processed.

3270 Data Stream Orders

An HCON display session supports these 3270 data stream orders.

Order Mnemonic Hex Line Code
Set Buffer Address SBA 11
Start Field SF 1D
Start Field Extended SFE 29
Modify Field Attribute MF 2C
Set Attribute SA 28
Insert Cursor IC 13
Program Tab PT 05
Repeat to Address RA 3C
Erase Unprotected to Address EUA 12

The 3270 data stream orders perform the following operations:

Set Buffer Address (SBA) Sets the current buffer address to the value specified in bytes 1 and 2. The display session supports 12-, 14-, and 16-bit addressing. The SBA format is:
Byte Content Description
0 X`11' SBA Order Code
1-2 X`....' New, Current Buffer Address
Start Field (SF) Starts a new field by placing a basic field attribute character at the current buffer address of the display. The buffer address is incremented by 1. The attribute position is displayed as a blank. The extended field attribute for this position is set to X`00'. The SF format is:
Byte Content Description
0 X`1D' SF Order Code
1 X`..' Basic Field Attribute
Start Field Extended (SFE) Enables the user to define the start of a field and to assign these attributes:
  • Basic field
  • Extended highlighting
  • Color
  • Programmed symbol
  • Background transparency

The attribute character is stored at the current buffer address. The buffer address is incremented by 1. Any attribute type not specifically defined in the SFE order has its value set to binary zeros. If Byte 1 contains X`00', all attribute types are set to the default value.

Byte Content Description
0 X`29' SFE Order Code
1 X`..' Number of Type/Value Pairs (N)
2 X`..' Attribute Type
3 X`..' Attribute Value
... ...
2N X`..' Attribute Type
2N+1 X`..' Attribute Value
Modify Field Attribute (MF) Enables the user to selectively change these attributes at the current buffer address:
  • Basic field
  • Extended highlighting
  • Color

The attribute types not selected in the MF order maintain the same values. The buffer address is incremented by 1. The MF format is:

Byte Content Description
0 X`2C' MF Order Code
1 X`..' Number of Type/Value Pairs (N)
2 X`..' Attribute Type
3 X`..' Attribute Value
... ...
2N X`..' Attribute Type
2N+1 X`..' Attribute Value
Set Attribute (SA) Enables the user to change these attributes at the current buffer address:
  • Extended highlighting
  • Color
  • Programmed symbol
  • Background transparency

The SA order also enables the user to set the same attributes to the default values. The specified attribute is associated with all subsequent data characters in the outbound data stream until another write-type command is transmitted or a new SA order changes the attribute. The SA format is:

Byte Content Description
0 X`28' SA Order Code
1 X`..' Attribute Type
2 X`..' Attribute Value
Insert Cursor (IC) Sets the current cursor position to the current buffer address. The current buffer address remains unchanged. The IC format is:
Byte Content Description
0 X`13' IC Order Code
Program Tab (PT) Advances the current buffer address to the address of the first character of the next unprotected field. If you issue the PT order when the current buffer address is the location of an attribute byte of an unprotected field, the buffer address advances to the next location within that field. If the PT order in the write data stream does not follow a command, order sequences such as WCC nulls are inserted into the buffer. The nulls are inserted from the current buffer address to the end of the field, even if the field is protected.

If issuing the PT order when the current address is the location of a protected field attribute, the current buffer address advances to the first unprotected position of the next unprotected field.

The PT order stops its search at the last character location of the screen buffer. If an unprotected field attribute with an associated unprotected character location is not found, the current buffer address is set to 0. If the unprotected field attribute found is in the last character location of the screen buffer, the current buffer address is set to 0.

If the PT order terminates at the end of the screen while inserting nulls, and a second PT order immediately follows, the new PT order continues to insert nulls from buffer location 0 to the end of the current field. The PT format is:

Byte Content Description
0 X`05' PT Order Code
Repeat to Address (RA) Stores a specified character in all buffer locations. The specified character is stored starting at the current buffer address and ending at (but not including) the specified stop address. When the stop address is equal to the current buffer address, the character is stored in all buffer locations.

When you specify extended highlighting or color attributes for the character, the attribute values are entered into the extended character attribute buffer as each repeated character is written into the data buffer. The RA format is:

Byte Content Description
0 X`3C' RA Order Code
1-2 X`....' Stop Address
3 X`..' Character to be Repeated
Erase Unprotected to Address (EUA) Inserts nulls in all unprotected character locations in the buffer. The nulls are inserted starting at the current buffer address and ending at (but not including) the specified stop address. The character attribute associated with each null character is set to X`00'. The stop address then becomes the new current buffer address.

When the stop address equals the current address, all unprotected character locations are erased. The EUA format is:

Byte Content Description
0 X`12' EUA Order Code
1-2 X`....' Stop Address

3270 Data Stream Outbound Structured Fields

The structured field is a format used to transport data. Outbound structured fields are data fields that are sent from the host to the local system running HCON.

The HCON write structured field (WSF) command (X`F3') transmits the outbound structured fields to the display session. You can issue a single write structured field command to send one or more structured fields.

WSF Command (X`F3') Structured Field 1 Structured Field 2 ... Structured Field n

The outbound structured field functions supported by an HCON display session include:

Function ID Code (Hex)

Byte 2 Byte 4
Read Partition: Query Query List 01 02 03
Erase/Reset 03
Set Reply Mode 09
Outbound 3270DS: Write Erase/Write Erase/Write Alternate Erase ALL Unprotected 40 F1 F5 7E 6F

The outbound structured field functions perform the following operations:

Read Partition Enables a host application program to ascertain the color, highlighting, usable area, reply modes, symbol-set, and other characteristics of a terminal. The format of the read partition structured field is:
Byte Content Description
0-1 L Length of this Structure
2 X`01' Read Partition
3 X`FF' Partition ID (PID)
4 TYPE X`02' X`03' Query Query Query List
5 Bits 0-1 B`00' B`01' B`10' B`11' Bits 2-7 B`000000' This byte is present only for: Query List (X`03') Q-code List (Bytes 6-N) Query Equivalent plus Q-code List All Query Replies (Reserved) (Reserved)
6-n Q-List List of Query Reply Codes (Present only for Query List)
Erase/Reset Erases the screen and resets the display session to implicit partition state using the default or alternate size, as specified in the structured field. The Inbound Reply mode is reset.

If byte 3 contains any value other than X`00' or X`80', the structured field is rejected with a negative response (in SNA) or an Op-check (in non-SNA). The format of the erase/reset structured field is:

Byte Content Description
0-1 X`0004' Length of this Structure
2 X`03' Erase/Reset
3 Bit 0: B`0' B`1' Bits 1-7: B`000000' Implicit Partition Size: Default Alternate (Reserved)
Set Reply Mode Specifies the reply mode required in all subsequent inbound data streams. The specified reply mode remains in effect until it is changed by:
  • Another Set Reply mode structured field, specifying a different reply mode
  • An erase/reset structured field
  • An erase/write or erase/write alternate command, or a structured field with the WCC bit 1 set to 1, causing a reset function

The format of the Set Reply mode structured field is:

Byte Content Description
0-1 L Length of this Structure
2 X`09' Set Reply Mode
3 X`00' PID
4 MODE X`00' X`01' X`02' Others Reply Mode being requested: - Field Mode - Extended Field Mode - Character Mode - (Reserved)
5-n A-List (present only if Mode is X`02') List of Attribute Types: X`41' : Extended Highlighting X`42' : Color
Outbound 3270DS Enables the user to direct the write commands and other structured fields to the display within a single transmission. The format of the outbound 3270DS structured field is:
Byte Content Description
0-1 L Length of this Structure
2 X`40' Outbound 3270DS
3 X`00' PID
4 CMND X`F1' X`F5' X`7E' X`6F' Others WR command EW command EWA command EAU command (Reserved)
5 WCC WCC Byte if Byte 4 is X`F1', X`F5', or X`7E'
6-n Data Write Data if Byte 4 is X`F1', X`F5', or X`7E'

3270 Data Stream Inbound Structured Fields

The structured field is a format used to transport data. Inbound structured fields are sent from the local system to the host system.

An HCON display session uses the Attention ID (AID) (X`88') to transmit the inbound structured fields to the host program. You can issue a single AID to send one or more structured fields.

AID (X`88') Structured Field1 Structured Field 2 ... Structured Field n

The inbound structured field functions supported by an display session include:

Function ID Code (Hex)

Byte 2 Byte 3
Inbound 3250DS 80
Query Reply: Summary Usable Area Character Sets Color Highlighting Reply Mode Distributed Data Management Auxiliary Device Implicit Partition Null 81 80 81 85 86 87 88 95 99 A6 FF

The format for each structured field includes:

Inbound 3270DS Enables the user to send data from the alphanumeric presentation layer to flow together with the graphic data. The format of the inbound 3270DS structured field is:
Byte Content Description
0-1 L Length of this Structure
2 X`80' Inbound 3270DS
3 X`00' Partition Identifier
4 AID Attention Identifier
5-6 CURSOR Alphanumeric Cursor Position
7-N DATA Orders and Data
Query Reply In response to the query from the host system, the display session responds with a series of structured fields, or query replies, which describe the device capabilities. The query replies include:
AID (X`88') Query Reply1 Query Reply 2 ... Query Reply n
Summary Lists the supported query replies used by the query list.
Byte Content Description
0-1 X`000D' Length of this Structure
2 X`81' Query Reply
3 X`80' Summary
4-C Q-Codes:

X`80' Summary

X`81' Usable Area

X`84' Alphanumeric Partitions

X`85' Character Sets

X`86' Color

X`87' Highlighting

X`88' Reply Mode

X`95' DDM

X`99' Auxiliary Device

X`A6' Implicit Partition
Usable Area Defines the size and characteristics of the screen.
Byte Bit Content Description
0-1
X`0014' Length of this Structure
2
X`81' Query Reply
3
X`85' Character Set
4 0-1 B`00' (Reserved)

2 B`0' EXSF Supported

3 B`0' Not a "HARD COPY" Device

4-7 X`3' 12/14/16-bit Addressing Allowed
5 0 B`0' Variable Cells Not Supported

1 B`0' Matrix Character

2 B`0' Value in Bytes 6-9 in Cells

3-7 B`00000' (Reserved)
6-7
X`0050' Usable Area Width
8-9
X`0018' Usable Area Height
10
X`00' Units for Measure: Inch
11-14
X`00020089' Horizontal PEL Distance
15-18
X`00020085' Vertical PEL Distance
19
X`09' Default Cell Width
20
X`0E' Default Cell Height
21-22
X`0780' Character Buffer Size
Character Set Defines the character set active for this session.
Byte Content Description
0-1 X`0006' Length of this Structure
2 X`81' Query Reply
3 X`81' Usable Area
4 X`02' Graph Escape Not Supported
5 `00' (Reserved)
6-7 X`090E' Character Slot Width and Height
8-11 X`00000000' Load PS Not Supported
12 X`07' Length of Following Descriptor
13-14 X`0000' PS Characteristics
15 X`00' Local Character Set ID
16-17 X`XXXX' Global Character Set ID
18-19 X`XXXX' Global Character Set ID
Color Describes the color features of the display.
Byte Content Description
0-1 X`0016' Length of this Structure
2 X`81' Query Reply
3 X`86' Color
4 X`00' (Reserved)
5 X`08' Number of Color Attribute Pairs
6-21 X`00F4' F1F1 F2F2 F3F3 F4F4 F5F5 F6F6 F7F7 Default is Green Identification Pairs
Highlighting Identifies the type of highlighting supported by the display.
Byte Content Description
0-1 X`000D' Length of this Structure
2 X`81' Query Reply
3 X`87' Highlighting
4 X`04' Number of Pairs
5-21 X`00F0' F1F1 F2F2 F4F4' Default is Normal Action Pairs
Reply Mode Reports the reply modes supported by the display.
Byte Content Description
0-1 X`0007' Length of this Structure
2 X`81' Query Reply
3 X`88' Reply Mode
4-6 X`000102' Field, Extended Field, and Character Modes supported
Distributed Data Manager Defines the distributed data manager characteristic. This characteristic is used by the file transfer protocol.
Byte Content Description
0-1 X`0000' Length of this Structure
2 X`81' Query Reply
3 X`85' Distributed Data Manager (DDM)
4-5 X`0000' Reserved
6-7 X`0000' Inbound Buffer Size (no limit)
8-9 X`0000' Outbound Buffer Size (no limit)
10 X`01' Number of Subset Supported
11 X`01' DDM Subset Identification
Auxiliary Device Defines the characteristic of the auxiliary device used by the file transfer process.
Byte Content Description
0-1 X`0006' Length of this Structure
2 X`81' Query Reply
3 X`99' Auxiliary Device
4 X`00' Reserved
5 X`00' Reserved
Implicit Partition Defines the default and alternate implicit partition size.
Byte Content Description
0-1 X`0011' Length of this Structure
2 X`81' Query Reply
3 X`A6' Implicit Partition
4-5 `0000' (Reserved)
6 X`0B' Parameter Length
7 X`01' Implicit Partition Size
8 X`00' (Reserved)
9-10 X`0050' Width of Default Implicit Partition
11-12 X`0018' Height of Default Implicit Partition
13-14 X`0050' Width of Alternate Implicit Partition
15-16 X`0018' Height of Alternate Implicit Partition
Null Defines the transmitted inbound in reply to a query list when the display session does not support any of the query replies in the list.
Byte Content Description
0-1 X`0004' Length of this Structure
2 X`81' Query Reply
3 X`FF' Null

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