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

*RESET PRIN TOUT START SOUND KYBD RESETBIT FOR MAT PRINT ALARM RESTORE MDTBITS 0 2 3 4 5 6 7Figure 6-4. WCC Byte FormatBitExplanation0,1 Used to make the WCC an EBCDIC/ASCII translatable character.32,3 Define the printout format, as follows:=00 - The CR, NL, FF, and EM orders in the data streamdetermine print line length. Provides a 132 columnprint line when orders are not present.=01- Specifies 40 column print line.=10 - Specifies 64 column print line.=11 - Specifies 80 column print line.4 Start Print bit. When set to 1, initiates a printout operation atcompletion of the write operation.SThe Sound Alarm bit. When set to 1, sounds the audible alarmat the selected device at the end of the operation if the devicehas an audible alarm.6 Keyboard Restore bit. When set to 1, restores operation of thekeyboard and resets the AID byte at the termination of the I/Ocommand.7 Reset MDT bits. When set to 1 all Modified Data Tag (MDT)bits in the selected device buffer are reset before any data iswritten or orders are executed.Figure 6-5. Write Control Character (WCC)This figure describes the function of each WCC bit. When the WCC specifies anoperation that does not apply to the selected device (for example, if the SoundAlarm bit is set and the selected device does not have an Audible Alarm), the specifiedoperation is ignored. When the WCC byte is followed by order or displaydata bytes, only the Reset MDT Bits function, if specified, is performed before thewrite operation; any other WCC function is deferred until all data is written and allorders are performed.Orders and buffer data follow the WCC byte. Buffer data can be written into anyspecified location of the buffer without erasing or modifying data in the otherbuffer locations. Data characters are stored in successive buffer locations until anorder is encountered in the data stream which alters the buffer address, or until allRefer to IBM 3270 Information Display System: Data Stream Programmer's Reference.Chapter 6. IBM 7171 I/O Interface to the Host System 6-5