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

Set Home Line, Set Left Margin, Set Column Tabs: There is one complex stringbeginning X' 2B5BE3 ' . These introducer characters are then followed by up to 30additional bytes of parameter data:Char#123-30FunctionHome line numberLeft margin columnColumn tab stopsEach byte is formed by the binary line or column number added to the X' 40 'blank character. Thus the sequence2B5BE34149494Fwould set home (X' 41') to the second row (first unprotected character position),the new line left margin (X' 49' )·to column 10, and tab stops at columns 10 and16 (X' 494F'). If the write buffer does not extend to include a full 28 tab stops,only the tab stops specified will be set. The host string fully replaces all previoustab stop settings. There is no way to merge new tab stops with existing tab stopsunder host control. If any value in this string is out of range or out of order the restof the string is ignored, but all values set up to that point are preserved.Set Mark: Using the special order string "Set Mark of 'xx' at Current BufferAddress," the host application can "overlay" a single character at the currentbuffer address on the screen with the "mark" character specified after the X' BO 'order. The mark is invisible to the host; a host read will only receive the actual"underlying" character.Clear Mark: With the special order string "Clear Mark," the host application canclear the mark previously set by the "Set Mark" order. After the mark has beencleared, the original contents of the screen position reappears.MUltiple Setup Format: It is possible to include several setup "orders" following asingle x' 2B5B' sequence by bracketing them with "$" (x' 5B') characters. It isimportant in this case to code each order string at its full length, since x ' 5B' couldalso occur as valid data within an order string. In other words, all 28 tabs must beincluded (even if they are x ' 40 ' ; see below).For example, the following extended setup order might occur imbedded in a writebuffer:HexChar.Labels2B5B5BC5B05BE34149494F5B4040 ... 405B$$E $T $ $E E B R M T H N t t t t t ... t BThe sequence begins with the special escape sequence (labeled E), followed by thefirst of the two bracketing characters (labeled B), then an order to restoreEnter/New Line (labeled R). Next is a Set Mark order (labeled M) followed bythe mark character ("$"), and finally, an order to establish Home (H), New Line(N) and column tabs (t t t ... ). Note that there must be exactly 28 tabs (since thisis a bracketed sequence) and that "$" may be one of them (meaning column 27).6-42 IBM 7171 Reference Manual and Programming Guide