Post by thread:Another way to do BCD

There is currently a discussion on the list regarding Binary to BCD conversion. For the sake of people who are new to programming I would just like to mention an alternative to Binary to BCD conversion: Accumulate the data in BCD to begin with! While this method is not always applicable, there are many cases where the binary value isn't used for anything except conversion to BCD. So why not set up some file registers as places to hold the Units, Tens, Hundreds, etc.? When you update the counter set you check for ten (0AH) and reset the current digit to zero and perform a carry. Indirect addressing gives you a simple way to move from digit to digit when a carry occurs. Such carrys can ripple through multiple digits when there are several '9's in a row. If a binary count is *also* desired, accumulate that in a separate binary counter file register set. This method works well if you have adequate time during accumulation of the counts to perform the BCD additions and carrys. As a further note, each 8 bit byte can hold TWO BCD nibbles, so storing a number like 999,999 only requires three file registers. The same methods can be used to store things like time-of-day which require certain digit sets to have modulo 60, modulo 12 and the like. While purists may turn up their noses at such techniques, these methods do have the advantage of being easy to understand and implement. Although not "optimal" solutions for all cases, they are easy for beginners to use, so they *do* have their place. Respectfully submitted for the sake of those who want to learn, Fr. Tom McGahee

part 0 935 bytes Definitely. Depending upon the application and the relative frequencies of displaying the data vs updating it, working with "native format" numbers can make many types of operations very convenient. On a somewhat related note, it's sometimes a good idea to configure the physical aspects of your system and/or sampling intervals to allow optimal numeric display. For example, if you have an motor tach input that pulses once each rev and you wish to display the motor speed in RPMx100, counting the number of pulses every 1/100 minute will be easier and more accurate than counting the number every second and multiplying by 0.6. Or, if you're trying to measure temperature with a 10mV/degC temperature chip/op amp feeding an A/D, it may be a good idea to adjust your op-amp's gain so that full-scale on the A/D is 640mV (to convert the A/D into temperature Celcius, just divide by four; no fractional maths required).