2.2 The IBM 7171 ASCII Device Attachment Control Unit - Index of

Setup Functions for Host Application ProgramsTransparent mode is ended by either a Master Reset sequence received from thekeyboard or a non-transparent write from the host. A non-transparent write is onewhich contains more than the WCC and does not begin with the transparent modeintroducer sequence. It is recommended that an application program issue a nontransparentwrite at the end before returning to the normal TSO or CMS environment.A null WCC followed by an SBA to the upper left corner (X I 40114040 I)will serve nicely to end transparent mode. If Transparent mode is ended by aMaster Reset from the keyboard or a Write command from the host, the devicescreen will not be cleared. If Erase/Write or Erase/Write Alternate is used, thenthe device screen will be cleared and operation will resume in the mode selected.Write/Reod: A second form of transparent mode is the "TransparentWrite/Read," which may be specified with either of the following SBA sequences:XI 115D7F110001 I or X ' 115D7F110005 1When this form is used, the IBM 7171 will enter transparent mode and transmit thedata to the device as in normal transparent write mode. When all data has beentransmitted to the device, all characters sent by the device in response will bereceived and saved. This receive is terminated by the receipt of an ASCII CarriageReturn, the Master Reset sequence as defined in the active terminal definitiontable, or by receipt of more than a screen sized buffer of data. Pacing stop (asdefined in the active terminal definition table) is also by default an ending conditionfor Transparent Write/Read, but this can be disabled by setting the X I 10 1 bitin the System Control Flags contained in NV-RAM. Refer to section 4.4.1, "DataArea 1 Layout" on page 4-20 for the location of the flags, and toChapter 9, "Special Maintenance Facility and System Messages" on page 9-1 forthe Maintenance Facility Display and Store commands required to set the flag.Upon presentation of the automatic attention interrupt, the host must perform aRead Modified command. Data will be returned in Read Buffer-like format. Anull AID X I E8 I will be followed by a cursor address pointing to the byte followingthe last received data, followed by the data in seven bit ASCII, with the X I 80 I bitset on in each byte. All input will be ignored during the transmission of the writedata, and all characters received during the read (including erroneous charactersand the terminating character) will be presented to the host. After the terminationcharacter is received, the terminal is left in transparent mode. If the 7171 inputbuffers are overrun by the device, then it will also present an Attention interrupt.The AID returned by the mandatory Read Modified will be X I E4 I to indicate theerror. Transparent Write/Read is intended for PC file transfer protocols or for. limited interactive functions such as reading crosshair positions on a graphicsdevice.The extended functions are mostly setup functions that can also be initiated from ahost application program using a special order. Special orders are defined using theconvention X I 2B I followed by a dollar sign ("$" or X I 5B I ) followed by one ormore characters. Additional setup functions defined specifically for use by hostapplication programs are described below. A list of the special orders available to ahost application program is shown in Figure 6-24 on page 6-41.6-40 IBM 7171 Reference Manual and Programming Guide