dat2343 summary of standard data encoding © alan t. pinck / algonquin college; 2003
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DAT2343
Summary of
Standard Data Encoding
© Alan T. Pinck / Algonquin College; 2003
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Character EncodingStorage Unit = byteASCII ‘A’:41h …’Z’:5Ah; plus 20h for lower case ‘0’:30h … ‘9’:39h blank:20h; carriage return:0Dh; line feed:0Ah
EBCDIC ‘A’:C1h … ‘I’:C9h; ‘J’:D1h …’R’:D9h;
‘S’:E2...‘Z’:E9h subtract 40h for lower case ‘0’:F0h … ‘9’:F9h blank 40h
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Basic Integer Numeric Forms
Storage Unit = wordUnsigned Binary position numbers (starting at 0 on right) position weights : 2position
2’s Complement subtract unsigned binary version of absolute
value from 0 (if working in binary) reverse bits and add 1
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Standard Integer Numeric Flags
Zero all bits in result word are 0 may not be a “true” zero e.g. AAAh + 556h (12-bit word) would turn Zero
“on”
Carry result wrong (too large or less than zero) for unsigned binary
Sign copy of left-most bit of result word
Overflow result is wrong if treated as 2’s complement (result sign is logically
impossible for given operand signs)
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Basic Float Form : 32-bit IEEE-754
1 bit : sign (0=positive; 1=negative)
8 bits: excess-127 binary exponent
23 bits : normalized binary mantissa without leading 1.0
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Hybrid Character-Numeric Forms
Zoned DecimalFd Fd … FD sd
BCD Packed Decimal (a form of BCD)
dd dd … dd ds(always an odd number of digits)
d: hex value in range 0 to 9 inclusive
s: C (hex) positive (also accepts A, E, and F as positive)
D (hex) negative (also accepts B as negative)
(sign is always in right-most byte)
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End of Lecture