All,
Been testing some custom boards we built around the Hercules 4357.
we shrunk our board down very very small to accomodate alot of HW on it.
we've been using the HET engine capabilites for some "critical timing stuff", that we run in parallel with the actual processor....(i.e. the HET runs independently as intended)
we dseigned in a 16.00000MHz crystal, mainly because the launchpad uses 16MHz and the part has 20MHz as max listed...so, didint want to run it to the MAX.
we set our load capacitance across the crystal based on the crystal data sheet....
we can run code...load/etc etc....basic "typcial C code" runs fine....
we've been running the HET engine stuff and we see differneces between our "counts" on the TMS570LC4357 launchpad and out custom board....very minute differences in the "counts" we look for.
Q: I looked at the crystal markings on the Launchpad....ECS D 160.......cant find BOM on launchpad...know this is an ECS 16MHz crystal and, from what I can see, the datasheet for this crystal is calling out 20pF for the Cload....why is the load capacitance 33pF on the launch?...was this selected at some point from testing?.......,.
reason I ask......we changed the load capacitance on our custom boards to something higher than the manufactueres data sheet....and out HET testing errors go away.......
I realize that the load capacatiacne will shift the resonant frequency slightly...(higher Cl , lower Fr....).....
I'm just looking for a "technical reason" for the selection of the launch CLoad, if there is one.....
I'm going to do some spectrum analyer investigation on our boards as well....
just hate having to rely on "that fixed it...ship it"...rather than having some scientific data
and again.....I appreciate this posting forum and the participants.....it/you have helped me immensely....
