| ??? 03/24/06 13:38 Modified: 03/24/06 13:41 Read: times |
#112964 - A very bad signal to beginners! Responding to: ???'s previous message |
Richard said:
I've been successfully building wire-wrapped high-speed (>80 MHz) digital circuits since the 'late '70's though, and never had a problem that couldn't be worked out. 1. Richard, you give a very bad signal to beginners! What works for a professional of many years of experience does not necessarily work for a beginner. Many beginners will read your lines now and think to themselves, hey why not using a wire wrap or bread board, when big Richard is using them all the time and never had any problems? I can tell you from my experience, that more than about 80% of all hardware problems come from an unsuited board. Because of resonances because of not having the signal traces routed over a solid ground plane, with the result of corruption of timing and violation of noise margins. 2. What worked successfully in the 70' need not necessarily to work today. Take care, todays microcontrollers and digital chip families are much much faster than in the old days. Transition times of output signals is what counts here, not so much the clock frequency of micro. Today you suffer from much more radiation, ground bounce, ground noise and especially deadly, if you have cables to leave the board, common mode noise. What worked with slow TTL-gates does not work with modern 74HCMOS: Only one 74HCMOS gate output signal not being routed properly as a transmission line over a solid ground plane can make your board fail the CE radiation test! We have tested this. So, it cannot be recommended at all to use a wire wrap board today! The neclecting of a proper mulitlayer PCB containing a solid ground plane will especially make problems, if you have to connect two boards via a cable link. Because then, heavy resonances of unpredictable wiring impedances will occur, totally eroding the timing and violating the noise margins. Not even mentioning that you will hardly pass the CE-radiation test with a wire wrap board! 3. You talk about "never having had problems, that could'nt be worked out". So, you epxerienced problems from time to time? But you could find a solution, because you are experienced, because you know, that at least a Vcc and ground plane is needed, because you know how to route the bus signals and how to route fast clock signals. I think that Zeeshan is neither having a board containing a ground plane nor a Vcc plane nor having enough experience to solve any problems. Why else has he posted here? The only signal given to Zeeshan should be, guy use a proper PCB! Kai |
