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Conversion of EBCDIC Addresses to Row Column Notation

IP.com Disclosure Number: IPCOM000084539D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Chaires, AM: AUTHOR [+2]

Abstract

In a data management system having user input via either the MOD 1 or MOD 2 display station, the row/column screen position is indicative of the nature of processing to be performed. It is thus necessary to convert the EBCDIC buffer address to row/column notation. Techniques are presented for performing this conversion for both the MOD 2 and MOD 1 screens. MOD 2.

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Conversion of EBCDIC Addresses to Row Column Notation

In a data management system having user input via either the MOD 1 or MOD 2 display station, the row/column screen position is indicative of the nature of processing to be performed. It is thus necessary to convert the EBCDIC buffer address to row/column notation. Techniques are presented for performing this conversion for both the MOD 2 and MOD 1 screens. MOD 2.

There is a cyclic relationship betveen EBCDIC buffer address codes and row/column screen positions. The high-order byte of the buffer address goes through 30 cycles of 64 positions each; i.e., line 1 column 1 line 1 column 64; line 1 column 65 - line 2 column 32;... line 24 column 17 - line 24 column 80. For each cycle of 64 the low-order byte of the buffer address goes through four cycles of 16 positions each, i.e., contiguous screen positions within the associated cycle of 64. Two tables CYCLE 64 and CYCLE 16 are generated to reflect this relationship. The former contains 30 pointers, one for the beginning of each cycle of 64. The generation of the CYCLE 64 table is shown below: ADDRESS = ADDRESS OF CYCLE 16 TABLE

DO FROM I = 1 TO 30 BY = 1

CYCLE 64 (I) = ADDRESS

ADDRESS = ADDRESS + 4 WORDS

ENDDO.

The code for generating the CYCLE 16 table, which contains 120 entries representing the five subcycles of 16 positions within each of the 24 rows of the screen is shown below: POINTER = 1

DO FROM I = 1 TO = 24 BY = 1

DO FROM J = 1 TO = 65 BY = 16

CYCLE 16 (POINTER) = I, J.

Row/column screen position is found by a technique using these tables and the EBCDIC address code. The entry point to CYCLE 64 is obtained by masking the high-order (row) byte of the address code with X'IF' and adding 1. The CYCLE 64 value thus accessed is the pointer to the beginning of the proper set of four row/column elements in...