1J3 (Display BCD - whatever that is?)

Not that it helps in any way with this problem, but for info and as it used a fair bit in pins, BCD is binary coded decimal.  You use 4 bits (a nibble) to represent a decimal number, so 0101 is equal to five, 1001 is equal to nine, etc. In BCD if you wanted to represent the decimal number 27 it would be 0010 0111, a two and a seven, but split along nibble  boundaries.  It's not very efficient for storage because within each nibble a few combinations don't map to decimal numbers. 1001 is 9 which is fine, but anything higher eg 1010, 1011 etc is wasted.  You also need "odd" hardware to any arithmetic  1001 numerically added to 0111 is 16 decimal which is 0001 0110 in BCD - the hardware exists, but is a bit of a frig.  1001 added to 0111 in normal integer arithmetic would be 10000

In pins it is used a fair bit for driving displays, at least in SS machines - I'm not familiar with DMDs. What they do is show the value of the digit to be displayed in BCD and then, by other means, indicate which digit is to be displayed. If you roll through every digit fast enough you can display the whole score.