BCD coding

The way in which the pH digits are used to form a complete binary coded decimal word is shown above.

Each pH digit is represented as one BCD 1-2-4-8 "nibble". The sum of the 1-2-48 BCD "bit weights" is equal to the decimal value of the digit. Two nibbles are combined to make an 8 bit "byte", and two bytes are combines to make a 16-bit "word" containing all four pH digits.

Since we never encounter pH values greater than 20, the most significant pH digit, for values over 9.99, are simply represented as a single bit. We will later combine it with other single bits to make a 5th nibble.

In this staff meeting, we will discuss how to use all of these bits to light LED's on the plastic experimenter's station. Notice that when the BCD nibbles are combined into a full word, the actual decimal value of the word increases to reflect the total number of bits in it.