>> H.C. Cron wrote >> >> HCC> As I see the problem, you can not solve it in your way. What you are >> HCC> doing can be compared with an inverter the output of which is fed >> HCC> back to the input. Look at D. D is a constituent of the Reset signal >> HCC> and just this Reset signal has to reset D by voltage levels (no edge >> HCC> triggering). This will result in the voltage of D to hang somewhere >> HCC> between the logic levels. >> >> are you really sure about that? >> You have a natural delay in Martin's circuit, since the D output will >> not instantaneously flip back to the high-state once the reset signal >> disappears, but only after 8 external clock signals.
HCC> How can you reset D with the D signal itself? These are level HCC> signals, no edge trigering. as long as the flip-flop of the D-output has not been reset, the output will stay in its 1-state. When the flip-flop has been reset and the output - after a certain output delay time (usually some ns), the output will go back into the 0-state, disabling the reset signal. The output and thus the reset signal will not - under any circumstances - take a metastable position in the middle of the supply voltage, as it does in the case of a feedback inverter, since a low on the reset does not automatically force the D-output back to the 1-state. It will stay 0 until a subsequent number of counts have passed the clock input of the counter. Since the flip-flops in these counters are essentially identical, a reset pulse sufficient to reset the flip-flop "D" will also suffice to reset flip-flops "A" to "C". This is furthermore insured, since the reset pulse is prolonged by the gate delay of the flip-flop "D" and will be active until "D" really toggles (the delay tpHL from the datasheet). This technique is referred to as "count truncation" in the datasheets (e.g. Fairchild 74hc393, TI 7490-93 Uwe. -- Author: Uwe Zimmermann INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
