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

the data has been entered. During the write operation, the buffer address isadvanced one location as each character is stored.The buffer location where data entry starts depends upon the following considerations:1. The starting location may be specified by an SBA order that follows the WCC.(This order is described later in this chapter under "Orders.")2. The starting location will be the buffer address containing the cursor if theWrite command is not chained or is not preceded in the chain by a Read orWrite.3. The starting location will be the current buffer address if the Write command ischained to a preceding Write or Read.The formatting and placement of write data and the modification of existing bufferdata are described under "Orders."Programming Notes:1. If the commands are being chained, the Write or Erase/Write command with theStart Print WCC bit set must be the last command in the chain. If not, the Writeor Erase/Write command that specifies Start Print will be aborted.2. The Printout Format bits are honored only if the Start Print bit is set in the sameWCC.Programming Restriction: A Write command should not be chained from an Erase AllUnprotected command. If it is, the operation is undefined. 4Erase/Write CommandExecution of the Erase/Write command performs two operations: an erase operationand a write operation. The erase operation clears the entire device buffer tonulls, positions the cursor to character location 0, and resets the buffer address too.Erase/Write then performs the write and WCC operations in the same manner as aWrite command.4 Refer to IBM 3270 Information Display System: 3274 Control Unit Description andProgramming Guide.6-6 IBM 7171 Reference Manual and Programming Guide