Electronics > FPGA

A 5V CPLD in 2023?

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NivagSwerdna:
I have a one-off (OK... a couple off project)... I need to replace a custom chip from an arcade game...

So the game is 5V TTL with a bit of custom silicon in a 28 pin DIP package.

I don't exactly know the functionality yet but I believe it to be simple... we can get to complexity later.

I know it has two 8-bit inputs.  i.e. 2x8 pins for data in

I know it has one 4-bit output.

I know it has 3 control lines.

So in total I need 16+3=19 ins and 4 outs.  All at 5V TTL.

For simplicity let's assume one line clocks all 16 inputs into a latch, and then the 2nd control line clocks out the 16 bits into the outputs 4 bits at the time.  The 3rd line determines the order the nibbles are clocked out (in sets of fours) either least significant nibble then up, or most significant nibble then down.

I could probably do this in 74 series logic but that's going to take a few devices and make it big...

Any suggestions?

(I would like something that isn't too obsolete but it is a home project so possibly could use old stock)

PS
I only have 4 outputs... so maybe something that was 5V tolerant on inputs and I could level shift the 4 outputs?  BTW... Operating frequency <2MHz

james_s:
Have you looked at the various projects out there already to do exactly this? Some use 5V tolerant parts, some use level shifters on the carrier board.

_pat_:
NivagSwerdna,

might I suggest that you cast your eyes over the Xilinx XC9500XL series ? Whilst 3.3V parts they have 5V tolerant inputs so could directly interface on that side.

On the output side you can either use dedicated level shifter devices or, given the relatively low speed and that there's only 4 of them, you could use discrete (or co-packaged) N-channel FETs (gate to 3.3V, source to CPLD, drain to pullup resistor to 5V, output is from drain).

Hope this helps,

Pat.

langwadt:
afaict XC9500XL is still available, it is 5V tolerant. If you system is really TTL threshhold is 2.4V so 3.3V is sufficient for output, else something like two 74HCT2G34 on 5V should do for 4 outputs

tchiwam:
Some level shifters fit neatly under a dip600 package while the fpga can fit on top. needs a 4 layer board but it makes it a near drop in.

Dip 300... need to get creative and go around the other components...

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