GA22-7000-4 IBM System/370 Principles of Operation Sept 1975
Page288(288 of 329)
I Bit Positions 0,1 I Bit Positions 2,3 ----+-----+-----1----;-----; 'm 0 ..,' .,.,' 'u "/:' ] 8 :;: ;;; 0001 DC2 FS SYN 0011 TM C RES BYP PN D M U 0101 NL LF RS N V BS ETB UC 0 W 0111 I L ESC EOT G X CAN Q Y 1001 EM Z 1010 CC SM 1011 CUI CU2 CU3 1100 IFS DC4 < % @ J 1101 IGS ENQ NAK 1110 IRS ACK > 'T 1111 9!rd Hole Pa!!erns CD 12-0-9-13-1 CD No Punches CD 12-0 ® 0-1 CD 12-11-9--8-1 CD 12 @) 11-0 ® 11-0-9-1 11-0-9-0-1 (]) 11 0-8-2 ® 12-11 12-11-0,·9-8-1 0 12-11-0 12 Special Graphic Characters ACK Ackn.mledge EOT End of Transmission PF Punch Off Cent Sign > Greater-than Sign BEL Bell ESC Escape PN Punch On Period, Decimal Point Question Mark BS Backspace ETB End of Transmission Block RES Restore < Less-than Sign Grave Accent BYP Bypass ETX End of Text RLF Reverse Li ne Feed Left Parenthesis Colon CAN Canc •• 1 FF Form Feed RS Reader Stop Plus Sign Number Sign CC Cursor Control FS Field Separator SI Shift In I Logical OR rq, At Sign CR Corrillge Return GE Graph i c Escape SM Set Mode & Ampersand Prime, Apostrophe CUI Customer Use 1 HT Horizontal Tab SMM Start of Manual Message I Exclamation Point Equal Sign CU2 Customer Use 2 IFS Interchange Fi Ie Separator SO Shift Out S Dollar Sign Quotation Mark CU3 Customer Use 3 iGS I nterchange Group Separator SOH Start of Heading Asterisk Tilde DCI Device Cantrall I L Idle 50S Start of Signi ficance Right Patenthesis { Opening Brace DC2 Devic:e Control 2 IRS Interchange Record Separator SP Space Semicolon J' Hook DC4 Device Control 4 IUS Interchange Unit Separator STX Start of Tex t "I Logical NOT 'I' Fork DEL Delete LC Lower Case SUB Substitute Minus Sign, Hyphen } Closing Brace OLE Data Link Escape LF Line Feed SYN Synchronous Idle / Slash \ Reverse Slant OS Digit Select NAK Negative Acknowledge TM Tape Mork Vertical Line Chair EM End of Medium NL New Line UC Upper Case Comma Long Vertical Mark ENQ Enquiry NUL Null VT Vertical Tab % Percent EO Eight Ones Unde.rscore 288 System/370 Principles of Operation
Appendix I. Number Representation and Instruction-Use Examples Number Representation FIXED-POINT WITH TWO'S COMPLEMENT A fixed-point number is a signed value, recorded as a binary integer. It is called fixed-point because the programmer de termines the fixed positioning of the radix point. Fixed-point operands may be recorded in halfword (16- bit) or word (32-bit) lengths. In both len-gths, the first bit position (0) holds the sign of the number, with the remaining bit positions (1-15 for halfwords and 1-31 for fullwords) used to designate the magnitude of the number. Positive fixed-poirit numbers are in true binary form with a zero sign bit. Negative fixed-point numbers are represented in two's-complement notation with a one bit in the sign position. In aU cases, the bits between the sign bit and the leftmost significant bit of the integer are the same as the sign bit (that is, 311 zeros for positive numbers, ql1 ones for negative numbers). Negative fixed-point numbers are formed in two's-comple ment notation by inverting each bit of the positive binary number and adding one. For example, the true binary form of the decimal value (+26) is made negative (-26) in the following manner: +26 Invert Add 1 -26 S Integer o 000 0000 0001 1010 1 111 1111 1110 0101 1 111 1111 1110 0110 (Two's-complement form) This is equivalent to subtracting the number 0000 0000 0001 1010 from 1 0000 0000 0000 0000 The following addition examples illustrate two's-comple ment arithmetic. Only eight bit positions are used. All negative numbers are in two's-complement form. 1. 2. 3. +57 +35 +92 +57 -35 +22 +35 -57 -22 0011 1001 0010 0011 0101 1100 0011 1001 1101 1101 No overflow. 0001 0110 Ignore carry-carry into high-order position and carry out. 0010 001l 1100 0111 1110 1010 Sign change only; no carry 4. -57 1100 0111 -35 1101 1101 No overflow. -92 1010 0100 Ignore carry-carry into high-order position and carry out. 5. -57 = 1100 0111 -92 = 1010 0100 -149 = *0110 1011 *Overflow-no carry into high-order position but carry out. 6. +57 0011 1001 +92 0101 1100 149 = *1001 0101 *Overflow-carry into high-order position, no carry out. The presence or absence of an overflow condition may be recognized by the condition of the carries. • There is no overflow: a. If there is a carry into the high-order bit position and also a carry out 2 and 4). b. If there is no carry into the high-order bit position and no carry out (examples 1 and 3). • There is an overflow: a. If there is no carry into the high-order position but there is a carry out (example 5). b. If there is a carry into the high-order position but no carry out (example 6). The following are 16-bit fixed-point numbers. The first is the largest 16-bit positive number and the last, the largest 16-bit negative number. Number 2 15 - 1 2° o - 2° _ 215 Decimal 32,767 1 o -1 = -32,768 S Integer o 111 1111 1111 1111 o 000 0000 0000 0001 o 000 0000 0000 0000 1 111 1111 1111 1111 1 000 0000 0000 0000 The following are 32-bit fixed-point numbers. The first is the largest positive number that can be represented by 32 bits, and the last is the largest negative number that can be represented by 32 bits. Number o Decimal 5 Integer 2147483647 = 0 111 1111 1111 1111 1111 1111 1111 1111 65 536 = 0 000 0000 0000 0001 0000 0000 0000 0000 1 = 0 000 0000 0000 0000 0000 0000 0000 0001 o = 0 000 0000 0000 0000 0000 0000 0000 0000 -1 = 1 111 1111 1111 1111 1111 1111 1111 1111 _21 -2= 11111111111111111111111111111110 _2 16 -65536= 11111111111111110000000000000000 _2 3i +1 =-2147483647= 1000000000000000 0000 0000 0000 0001 = -2147483648 = 1 000 0000 0000 0000 0000 0000 0000 0000 Appendix I. Number Representation and Instruction-Use Examples 289