The western 74141 and its Russian equivalent (K155ID1) are truly old fashion TTL parts. If you ever look at an old TTL databook, there are some common TTL specs:
Input logic-0: 0.8V or less Input logic-1: 2.0V or higher Output logic-0 (tied to 10 like inputs): 0.4V maximum Output logic-1 (same): 2.4V minimum TTL inputs naturally float high, to a level of ~1.6V. It registers this as a logic-1, but its prone to noise, hence it they like you to at least drag it up to 2.0V. The current draw is also asymmetrical. To pull it high (logic-1), only ~40uA (0.00004A) flows into the input, but drag it down to a logic-0 (low) and it will draw 1.6mA (0.0016A) from the input. Roughly 40x more low, than high. This also makes putting 1K resistors in series with their inputs. 1K*1.6mA translates to 1.6V, so the output of your uC, low (0V) or high (3.3V), may just look like a logic-1 to the TTL device (74141). The best thing is to use two supplies: +5V & +3V, and make sure the +3V turns ON first. Since your using a large uC, use one of its IO bits to turn on the +5V supply. Before that supply is turned ON though, make all the outputs between the uC and the 74141, low. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
