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

To continue the search for an unprotected field, a second PT order must be issuedimmediately following the first one. Since the current buffer address was reset to 0by the first PT order, the second PT order begins its search at buffer location o. Ifthe previous PT order was still inserting nulls in each character location when itterminated at the last buffer location, the new PT order will continue to insert nullsfrom buffer location 0 to the end of the current field.Repeat to Address (RA) Order: The RA order stores a specified alphameric or nullcharacter in all buffer locations,· starting at the current buffer address and ending at(but not including) the specified stop address. This stop address and the characterto be repeated are identified by the bytes immediately following the RA order inthe write data stream, as follows:BYTE0 RA Order1 Stop Address (byte 1)2 Stop Address (byte 2)3 Character to be repeatedOR0 RA Order1 Stop Address (byte 1)2 Stop Address (byte 2)3 Graphic Escape4 Character to be repeatedFigure 6-8. Repeat to Address (RA) Order FormatsThe third character (fourth if the third is Graphic Escape) following the RA orderis always interpreted as the character that will be repeated. If an invalid stopaddress is specified, the write operation is terminated at this point without storingthe character, and error status is generated.When the stop address is lower than the current buffer address, the RA operationwraps from the last position in the buffer to the first. When the stop address equalsthe current address, the specified character is stored in all buffer locations.Attribute characters will be overwritten by the RA order if they occur before theRA order stop address.Erase Unprotected to Address (EUA) Order: The EVA order inserts nulls in allunprotected buffer character locations, starting at the current buffer address andending at, but not including, the specified stop address. This stop address is specifiedby two address bytes which immediately follow the EVA order in the writedata stream. If an invalid address is specified, the write operation is terminated atthis point and error status is generated.When the stop address is lower than the current buffer address, the EVA operationwraps from the last position the buffer to the first. When the stop address equalsthe current address, all unprotected character locations in the buffer are erased.Attribute characters are not affected by the EVA order.6-10 IBM 7171 Reference Manual and Programming Guide