Re: Choice between CMOS 4099 or 74HC259

antedeluvian wrote:
> MM,
>
> The way I understand your question is that you want to replace a 74HC259
> with a 4099. If this is the case, then you should know that aside from
> anything else, they are not pin compatible. Secondly the Clear function
> appears to be inverse between the devices.
>
> Digikey seems to have plenty 4099s, so you don't need a circuit redesign.
>
> Generally you need to consider several things when replacing one technolgy
> with another. Firstly the setup times and write times are normally much
> longer in 4000 series CMOS. The 74HC series is quicker so you probably
> could make the substitution (if pin equivalent), but you do need to make
> sure the timing is OK.
>
> Driving 4000 series from any TTL output normally requires a pull up
> resistor to ensure logic high level compatibilty (provided they are both
> run from 5V) unless the 4000 series device has Schmitt trigger inputs
> (which the 4099 does not). Drive levels of the 4000 series into TTL can
> prove problematic. You need to investigate the output drive capabilty of
> the CMOS part.
>
> The 4000 CMOS series can operate with a supply voltage from 3V to 15V.
> This can be advantageous in some circumstances, but obviously interfacing
> with 5V systems would need extra attention.
>
> -Aubrey

Thanks for that, Aubrey. Okay, I now have found Cricklewood Electronics
that also do the 4099. Like I said, I'm a novice so when some of the
main catalogues didn't stock it I assumed it had become outdated and
little sought after.

By the way, the 4099s will be driving LEDs, one per pin. This is in
conjunction with MIDI.

Since I'm here, what's the next best choice to the 16F628(A)? I was
intending to use it in preference to a 16F84 because the former comes
with an inbuilt USART. However, that utilises RB1 and RB2 as RX/TX
respectively, which thus lose me those pins as outputs. Pin 8 (RB2/TX)
apparently cannot be configured as a bog-standard output when the USART
is invoked, even if TX is not required. And all the other pins that
could be outputs are already used up.

Therefore I am now considering the 16F877 instead, which has many more
pins to play with. However, this PIC is twice the price and has a lot
of additional functionality/capacity that I don't need. Is there
something in between? For example, do any of the 28-pin PICs have a
USART?

MM

.

Relevant Pages

  • Re: Choice between CMOS 4099 or 74HC259
    ... they are not pin compatible. ... >> longer in 4000 series CMOS. ... >By the way, the 4099s will be driving LEDs, one per pin. ... >apparently cannot be configured as a bog-standard output when the USART ...
    (comp.arch.embedded)
  • Re: ESD problems with PIC 16F88
    ... data on the Rx pin of the USART. ... This is a general rule for all CMOS logic - tie any unused inputs ...
    (comp.arch.embedded)
  • Re: ESD problems with PIC 16F88
    ... in a manner suggesting that it has received some random data on the Rx ... pin of the USART. ... tie the MCLR Pin to High. ...
    (comp.arch.embedded)