OFF TOPIC: VHDL Help needed!

[Sean_Goddard]

Hi All, I have a simple schematic which I want to put into a SMALL FPGA. Is there anyone out there who can help please?

BTW, one of the outputs is O/C and I'm not sure how to do this in VHDL.

Schematic is attached.

The outputs of U3 is normal, U5 MUST be Open Collector! All resistors are EXTERNAL to the device. The switch was for test purposes ONLY, and obviously the battery is for simulation purposes ONLY.

U1 = 74HC112
U2 = 74HC08
U3 = 74HC08
U5 = 74HC03

U4 was removed as surplus!

[Qiaozhi]

Hi All, I have a simple schematic which I want to put into a SMALL FPGA. Is there anyone out there who can help please?

BTW, one of the outputs is O/C and I'm not sure how to do this in VHDL.

Schematic is attached.

The outputs of U3 is normal, U5 MUST be Open Collector! All resistors are EXTERNAL to the device. The switch was for test purposes ONLY, and obviously the battery is for simulation purposes ONLY.

U1 = 74HC112
U2 = 74HC08
U3 = 74HC08
U5 = 74HC03

U4 was removed as surplus!

I haven't done any VHDL for a while, but I think you need to define the output port as "inout std_ulogic".
The easiest solution would be to generate structural VHDL directly from the schematic. Doesn't the FPGA vendor supply any free tools to do that?

[mikebg]

For beginners:
http://www.fpga4fun.com/
http://vhdlguru.blogspot.com/p/vhdl-faqs.html

[bklein]

I don't get why you would want a fpga - which btw there aren't small ones - for this.
Are you looking for small size? Then use SMD type logic parts. Or something like a PIC10F or the like. FPGA's are best for integration of thousands of logic gates not a handful. And you don't get resistors...