Tom Brandon wrote: > Don't mean to nit pick but I would have thought the SX was more > deterministic than a PC. True a SX may have non-deterministic jitter bu= t > that's about it. While any system with a cache like a PC is very > non-deterministic as depending on the last instruction executed (well, = the > data it used anyway) an instruction could take more or less time. = I'm not sure where you got your imformation, but the Scenix SX has an exa= ct interrupt response time, which can be translated to jitter-free. This mea= ns that after an interrupt occurs, there will be a fixed number of cycles (a= nd always the same number of cycles!!) until the interrupt is serviced. A PI= C on the other hand, does not have a jitter-free interrupt response. Try creat= ing an exact frequency of square wave output on a PIC, using the hardware tim= er interrupt as it's time base, and it will have jitter. = > Also I would have thought that interupts on a PC would have jitter just= like As a PC's processor can have an instruction currently being executed that= could take any number of clock cycles, how can there be a fixed number of= cycles to respond to an interrupt? > a Scenix. In fact it would have more absolute jitter as interupt trigge= rs > are much the same length (near instantaneous) while instructions are a = lot > smaller. Hence, the same 5ns jitter would be 10-20x more instructions. > = > Tom. Also, the word 'determinism', put in the context that it being used in th= is discussion, means everything occurs in a fixed number of clock cycles - instructions, internal and external interrupts, etc. Also, if there is a concern about exactly when an input captured, there is a SYNC function wh= ich can be enabled on the SX to syncronize the input capture to the system cl= ock. The output is always written on the rising edge of the clock. ____________________________________________________________________ Get free email and a permanent address at http://www.amexmail.com/?A=3D1 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use mailto:listserv@mitvma.mit.edu?body=SET%20PICList%20DIGEST