31600Re: [midatlanticretro] RS232 Again?
- Jul 11, 2013On Thu, Jul 11, 2013 at 11:32 AM, RonK <rkushnier@...> wrote:
I thought you guys could appreciate this.
I've been trying to "unbrick" a Seagate SATA 750 GB barracuda hard drive. The recommended approach is to go through it's 4-pin jumper connector to reach its serial port. http://www.overclock.net/t/457286/seagate-bricked-firmware-drive-fix-with-pics/240#post_20364127
It's "Back to the Basics" of RS232 technology. Oh no! Would I really have to open that trapdoor in my brain that I hadn't accessed for thirty years, and pull out all the old stuff? I guess so. Baud rate, Parity, STOP bits, Flow Control- oh all that wonderfulness... here again!The interweb has plenty of info out there to help with this. There really isn't any mystery to the interface. After a few min of searching for Seagate serial port, it clearly defines this to be a TTL level interface. Even the com settings are defined - just pop the settings into your terminal pgm and go. And the RS232 - TTL converters cost only a few bucks.
My main concern though, were the required voltage levels. It seemed that the Seagate drive wanted TTL levels. So it was recommended that the use of an RS232 to TTL adapter be employed. I didn't have one of those, but I did have a USB-to-RS232 adapter. I figured that unless the adapter employed some sort of voltage doubler to get the voltages up to the normal Rs-232 levels, I would be safe with the 5 volt USB power. Well that didn't work. See my overclock post above for more details.This is where you can find some info about the Seagate serial port being only TTL and addt'l instruction to access the Seagate drive.The fact that the MAX232 level converters are inverted is a non-issue. This is part of the RS232 standard. A Mark signal, negative level, is a logic "1' and vice versa - this conversion is done transparently in hardware. This is why it's important to use the correct adapter. And why you want a RS232 to TTL adapter - convert RS232 levels to TTL levels and not the other way around. With the USB to RS232 adapter, you are converting TTL levels ( albeit differential on USB) to RS232 levels - which is the opposite.As for the RS232 to TTL adapter, you can find them easily online for only $5 and free shipping, even on eB@yAnd you could even build one with only 2 transistors, a few resistors and a diode.Dan
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