Hello!

I'd be interested to hear from anyone who has used the XTAL2 output as a timing reference on an 8052 based system.

I have an 8051 datasheet which shows various timing diagrams (ALE, RD/WR, PSEN, P0,P2) relative to XTAL2. The datasheet also has the following caveat: "The AC Timings section of the data sheets do not reference any
timing to the XTAL2 waveform. Rather, they relate the critical edges
of control and input signals to each other."

My observation of the assertion of the control lines (RD/WR etc) shows that these are asserted on the opposite edge of XTAL2 than is shown in the datasheet. Specifically, the datasheet shows RD and WR being asserted on the falling edge of XTAL2, but it actually occurs on the rising edge (and no, I don't have the 'scope channel inverted!) Perhaps this is how you're supposed to interpret the caveat, in which case I guess I've answered my own question...

However, my concern is that, is it therefore safe to assume that RD/WR is always asserted on the rising edge of XTAL2?

Has anyone any experience of this?

Many thanks,

David