[sdiy] converting output from a RAM to CMOS

[mark verbos]

Thanks Dave, that makes sense then. It was working fine, I switched to  
a variation on the Deltalab idea and it appears to be working now.  
Bonus is, only passives between 'em.

Mark






On Jul 29, 2009, at 2:58 PM, Dave Manley wrote:

> mark verbos wrote:
>> I'm doing a module where all the logic is CMOS at 15 volts, but  
>> there are some 4164 RAM chips running at 5 volts. Getting control  
>> signals and data into the RAM is easy enough, using a 4049 powered  
>> from +5, but I'm having a little trouble getting back to 15 volts.  
>> I used a 2N3904 with a 4.7k resistor to the base and a 10k from the  
>> emitter to ground, power to collector and took the output from the  
>> emitter. The data at the RAM seems to be drained, as it slews back  
>> to ground at each step. What gives? Does it need a pull up  
>> resistor? Am I loading the output?
>
> It sounds like the output might be going high impedance.  Look at  
> the timing of CAS and the output slewing back to ground.  When CAS  
> is deasserted, the data out pin is tri-stated.
>
> -Dave
>
>