Difference between revisions of "Binary coded decimal"
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Revision as of 21:22, 16 November 2012
Binary coded decimal (BCD) is a method by which 4bit numbers are represented in digits 09, not 0F. In the F8, BCD numbers can be added together using ASD or from memory using AMD (there is, however, no AID opcode, BCD Add Immediate). In a single byte, two digits can be stored, and the appropriate carry flags set if the number rolls over 99. Each digit is coded as the number + 6, so 0 should be loaded as 6, 1 as 7, 2 as 8, etc. This table shows the encoding for individual digits:
Digit  4bit Value  0  %0110 1  %0111 2  %1000 3  %1001 4  %1010 5  %1011 6  %1100 7  %1101 8  %1110 9  %1111