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

4.2 How to Specify Terminal Information.There are two ways for a user to specify terminal information. They are:• Via an automated program• Via the Maintenance Facility.Automated ProgramAn interface exists for a user created program to automatically access and storedata into memory. For details, refer to Appendix D, "Interface for User SuppliedTable Modification Program."An implementation of this interface is supplied with the IBM 7171 and isdescribed in Appendix C, "IBM 7171 Support Utility for Modifying TerminalTables."Manual Table EntryThe second way to enter terminal information is by using the MaintenanceFacility. The Maintenance Facility allows the user to directly modify RAM andNV-RAM. For instructions on use of the Maintenance Facility, refer toChapter 9, "Special Maintenance Facility and System Messages." The usershould read and understand this chapter fully before entering the terminalinformation.Note: Anyone choosing to create a table generating program, or planning to manuallycreate or modify any existing terminal table MUST have working knowledgeof the following concepts which apply to IBM 7171 memory:1. Memory addresses are given as a SEGMENT and an OFFSET. For theNV -RAM, the segment will always be X' DCDD '. When an offset is given byitself, a segment value of X ' DCOD' can be assumed.2. Addresses and word values are stored byte reversed in memory. If an addressor word X' 1234' is known to exist at memory location X' 5678', the twobytes will be reversed. That is, the byte at address X' 5678' will be X' 34'and the byte at X' 5679' will be X' 12'.3. Table addressing in the 7171 frequently uses pointers. For a definition of theimplementation of these pointers, refer to 4.4.2, "Ports Area Layout" onpage 4-21.Chapter 4. Customizing IBM 7171 Tables 4-3