Plain TTL, or even LS TTL is as old and outdated as 4000 CMOS and they chew
current as well. There are a multitude of devices you can use in the 74
format though. Even the 74HC series will be better from current sink point
It all depends what you want to accomplish as part of the bigger picture.
If this is part of self education and you need easy access to parts, by
all means use 74HC parts.
If you want more esoteric latching parts with higher drive capabilty, try
looking at some parts by Allegro
Texas Instuments and ON Semi used to make compatible stuff, I am not sure
if they still do. Try also ST and Philips as well. They sometimes have
some very interesting devices for esoteric applications.
>> Take a look at this URL fro 28pin PICs. Scroll down looking for UARTS.
>> lot depends on the range of temperature you are going to operate in
>> what voltage you can let the output rise to (in the case of current
>> The outout voltage will increase as the current increases. If you are
>> the output to drive other logic, this can prove a problem.
>No, the 4099 would drive just LEDs, up to eight, one per output.
>> Using the TI data sheet, assuming that you are only operating at 25
>> and that you are sinking current through the LED, you will need a
>> of ((5-0.4)/0.51)Kohms in series with the LED. The device can sink
>> guaranteed in the above circumstance with a 5V supply. I doubt you
>> even see a dull glow from a "bog standard" LED. You may want to try
>> current devices like the HLMP1700 which can work down to 0.5mA within
>How about if a TTL chip were used instead of a CMOS? Mind you, I'm sure
>I've hooked up an LED to a CMOS output in the past (with resistor) and
>there's not been a problem.