Interfacing TTL and CMOS logic

[Gene Zumchak]

JBV,

    You need an octal open collector driver and a SIP pullup package.  You
ought to be able to find one that is non-inverting if that's important, or
you can just invert in your 8051 code.  A typical kind of chip is the old
ULN2001, at less than a buck, but I'm afraid that and its closest relatives
are septal, not octal.  The place to look is Allegro (allegromicro.com).

Gene Z


jbv wrote:

> Hi there,
>
> I'm back to this list with a slightly off-topic question.
>
> I need to drive a logic CMOS IC from a TTL source (actually a port of a
> 8051).
> The power supply of the TTL source is +5V, while the CMOS IC is +15V.
> Of course, direct interfacing is impossible, especially because the
> 'positive' level of the TTL
> output (typically 3.5V) is not sufficient for the CMOS. So I need to put
> some buffer in between.
>
> I found out that the 4049 (sextuple buffer) converts signals up to +15V
> into +5V TTL regular
> signals. So I imagine that there must be some equivalent buffer to
> convert 0/5V TTL signals
> into 0/+15V CMOS signals. And I don't have any CMOS databook at hand
> (everywhere I ask, it
> seems to be unavailable or sold out...)
>
> Important : I have very little room left on my PCB, and that's why I'm
> looking for a one-chip
> solution (no extra resistors, etc.).
>
> I also read somewhere that pull-up resistors connected between the TTL
> outputs and the VCC
> would be a workable solution... But to which VCC : +5V for TTL ics, or
> +15V for CMOS  ics ?
>
> Any suggestion ?
>
> jbv