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* NAME: (PAL-AP) DOC. 70180311000 REV.H PAGE 4

0129 * THE LOADER ON THE FRONT OF THE TAPE WILL LOAD ITSELF AND 0130 * THEN WILL LOAD THE PAL-FORMAT PROGRAM. 0131 * 0132 * 0133 * DATA IS PUNCHED IN BLOCKS OF 50 WORDS EACH. SALIENT 0134 * CHARACTERISTICS OF THE BLOCK STRUCTURE AREA ARE AS FOLLOWS: 0135 * 1) A START OF MESSAGE CHARACTER (OCTAL 201) IS 0136 * PUNCHED AT THE BEGINNING OF EACH BLOCK. 0137 * 2) FOLLOWING THIS. THE ADDRESS OF THE FIRST MEMORY 0138 * LOCATION IS PUNCHED. 0139 * 3) EACH BLOCK IS ENDED BY: 0140 * A) A CHECKSUM. THIS CONSISTS OF A WORD WHICH 0141 * IS THE EXCLUSIVE OR OF ALL WORDS PUNCHED 0142 * PLUS A WORD COUNT AND A BLOCK COUNT. 0143 * (THE FIRST BLOCK IS ZERO AND EACH ONE THERE- 0144 * AFTER IS INCREMENTED BY ONE.) THE 0145 * CHECKSUM IS ROTATED RIGHT ONE BIT EACH 0146 * TIME ANOTHER WORD IS ADDED TO IT. 0147 * B) AN END OF MESSASE CHARACTER (OCTAL 223). 0148 * THE EOM IS FOLLOWED BY A RUBOUT CHARACTER (OCTAL 377) 0149 * 4) SIX FRAMES OF LEADER ARE PUNCHED BETWEEN BLOCKS 0150 * AND TWELVE INCHES OF LEADER ARE PUNCHED 0151 * AT THE BEGINNING AND END OF THE PROGRAM. 0152 * 0153 * THE FORMAT OF THE PUNCHED WORDS IS AS FOLLOWS: 0154 * 1) NON-ZERO WORDS ARE PUNCHED IN "INVISIBLE CODE". 0155 * EACH 16-BIT WORD IS WRITTEN AS A FOUR-BIT AND 0156 * TWO SIX-BIT CHARACTERS ON TAPE. THE FOUR-BIT 0157 * CHARACTER REPRESENTS THE HIGH-ORDER FOUR 0158 * BITS 0F THE WORD. EACH SIX-BIT CHARACTER 0159 * HAS THE HIGH-ORDER BIT IN CHANNEL EIGHT AND THE 0160 * FIVE LOW-ORDER BITS IN CHANNELS FIVE THROUGH 0161 * ONE. ORDINARILLY, NOTHING IS WRITTEN IN CHANNELS 0162 * EIGHT THROUGH FIVE OF THE FOUR-BIT CHARACTER 0163 * OR IN CHANNELS SIX AND SEVEN OF THE SIX-BIT 0164 * CHARACTERS. 0165 * 2) EIGHT CHARACTERS CAUSE SPECIAL ACTION BY THE ASR. 0166 * THESE ARE 023 AND 223 (X-0FF). 021 AND 221 (X-0N), 012 0167 * AND 212 (LINE FEED), 005 AND 205 (WRU). THESE ARE 0168 * TRANSLATED INTO 177 AND 377, 176 AND 376, 175 AND 0169 * 375, 174 AND 374, RESPECTIVELY. IN THE CASE OF EACH OF 0170 * THESE CHARACTERS, CHANNELS SIX AND SEVEN ARE PUNCHED, 0171 * 3) WHEN ONE OR MORE CONSECUTIVE ZERO WORDS ARE 0172 * ENCOUNTERED IN MEMORY, THEY ARE REPRESENTED BY 0173 * ONE PUNCHED WORD. THIS CONSISTS OF THE TWO'S COMPLEMENT 0174 * OF THE NUMBER OF CONSECUTIVE ZERO WORDS ENCOUNTERED. IN 0175 * ORDER TO DISTINGUISH THESE Z-COUNT WORDS, CHANNEL EIGHT 0176 * OF THE HIGH-ORDER (FOUR-BIT) CHARACTER IS PUNCHED 0177 * 0178 *
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