This is an interesting side note for fanatics. You can skip this if you are not a fanatic.<\/p>\n
NOTE: If you have a HP97 don’t use non-normalized numbers (NNNs).
\nThe HP97 is a printing version of the HP67. NNNs burn out the print head on a HP97.<\/p>\n
The HP calculators used binary coded decimal (BCD) to fit numbers into registers (X, Y Z, T) and into memories.
\nInternally, numbers were stored in SCIentific notation with a 10 digit mantissa and a 2 digit exponent. When you add a sign to the mantissa and to the exponent you end up with 14 BCD digits: SMMMMMMMMMMSEE. S is 0 if the mantissa or exponent is positive and 9 if negative.<\/p>\n
14 BCD digits occupy 15 display positions as the decimal point is always right of the first mantissa digit and, on the HP67, a decimal point occupies a display position of its own.<\/p>\n
BCD defines meanings for 0-9 but each four-bit nibble can also hold other values (0x0a – 0x0f in hexadecimal notation).
\nThe display uses values outside of 0-9 to display the messages you see such as “Error” and “Crd”.<\/p>\n
Nibble values in registers display as: 0-9 = 0-9; A = \u201cr\u201d, B= \u201cC\u201d, C=\u201do\u201d, D=\u201dd\u201d, E=\u201dE\u201d, F=\u201d \u201c.<\/p>\n
The 14 BCD digits occupy 7 bytes of memory. Each program step occupies 1 byte (even if it is 3 keystrokes).<\/p>\n
One way of creating NNNs was to key in program steps, write these to a mag card and then write a data header over the start of the card (f W\/Data, insert card, turn the calculator off midway through the write). You could then load the card back in, as data, and see what appeared in the storage registers.<\/p>\n
A more interesting way involved getting the program counter outside of steps 000-224 (it would point into a storage register) and then keying in program steps there.<\/p>\n
See also: This is an interesting side note for fanatics. You can skip this if you are not a fanatic. NOTE: If you have a HP97 don’t use non-normalized numbers (NNNs). The HP97 is a printing version of the HP67. NNNs burn out the print head on a HP97. The HP calculators used binary coded decimal (BCD) … Continue reading The HP67 and Non-Normalized Numbers<\/span>
\nHoly Joe<\/a>
\nmy notes from 22 Dec 2005<\/p>\n","protected":false},"excerpt":{"rendered":"