Q. Sometimes during boot I see a lot of garbage data on the serial port. What's going on?
This probably has to do with oscillation of the serial level shifters during boot. The boot state of the CPU GPIOs is typically as inputs. For serial lines driven by CPU GPIOs, this means that the inputs to the level shifters are left floating until the drivers are initialized. We've learned that some EIA-232 level shifters go into oscillation when their inputs are not driven.
Q. So what's the solution?
Our current boot code initializes and drives the serial output lines early in the boot process (e.g. GC Plus CE boot code 1.81, Bitsy CE boot code, etc). If this issue affects your application, check to see if updated boot code is available on these forums for your product that resolve this issue. If not, email us with details about what product and operating system you're using and details of how this issue affects your application, we'll be glad to work with you to resolve this issue.
Q. I've noticed that only some of my systems seem to have this problem. Why is that?
This probably has to do with manufacturing variations in the serial buffers populated on your system. We have found that different batches and manufacturers of the same part acted differently.
For example, one GC Plus customer in early 2003 found that Sipex SP3232ECT buffers with a date code of 0025 worked well, but that parts with a date code 0150 (manufactured 1.5 years later) had the problem with oscillation.
In either case, updating the boot code eliminates this issue.
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Garbage Data on Serial Port During Boot
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Posted - 19 Jan 2004 : 11:37:06
