On Thu, Sep 22, 2005 at 08:06:13PM -0400, Dan McMahill wrote: > > Lets not even talk about ECL parts where VCC is 0 volts and VEE is -5.2 > volts. "Hey, how come all the 10H116's on my board are smokin' hot?" > > Also, mixed supply designs are common. If you make a 3.3V logic part > with implicit "VDD" power and you also have some 1.8V logic which also > uses implicit "VDD", you've got problems in the form of a magic smoke leak. > > Implicit power connections are evil! The only place were I don't think > so is DJ's example of the actual ground symbol or an actual VDD symbol. > But there, you're paying attention. > > -Dan >
My single board computer has 1.2V, 1.8V, 2.5V, 3.3V, 5.0V and 12V. The DSPcard is better with "just" 1.2V, 2.5V and 3.3V. Implicit power connections are something I have never used due to multiple supplies. I have recently switched to using seperate power symbols for some large components due to high power and ground pin counts (Spartan 3 FT256 has 28 ground balls and 40 power balls with 3 supply voltages). This works well for me and I may even extend it to smaller parts in future designs. -- Darrell Harmon http://dlharmon.com/dspcard Credit card size DSP/FPGA board
