68HC705 - OTP? - Page 1
Forum section: electronics / general

author: grumpydoc
author_rank: Super Contributor
timestamp: December 19, 2012, 03:14:03 pm
content: Picked up a few bits of industrial control stuff to go in the junk box. Lots of useful if old hat stuff - 68HC11's (external ROM versions) a couple of 32Kx8 UVEPROMs, some 32Kx8 SRAMs, lots of DACs and ADCs, relays and op amps, most of it socketed (bonus!). In fact I feel an 8 bit project coming onAnyway amongst the bits and pieces were 4 68HC705's - just to check these are OTP versions aren't they? so I might as well bin them unless I like the code that's already there (pretty unlikely).

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 19, 2012, 03:37:16 pm
content: I have an unused HC705 dev.kit somewhereIIRC there were a couple of EPROM versions in the box, e.g. windowed.

author: grumpydoc
author_rank: Super Contributor
timestamp: December 19, 2012, 03:44:35 pm
content: The ones I have are definitely not windowed.

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 19, 2012, 03:55:20 pm
content: I still don't know what to do with the kit, it's never been used but it's obsolete stuff. Oh well, maybe I just should bin it

author: grumpydoc
author_rank: Super Contributor
timestamp: December 19, 2012, 04:17:03 pm
content: ebay?

author: Lightages
author_rank: Unknown
timestamp: December 19, 2012, 04:42:40 pm
content: I might be wrong, but I seem to remember some of the series not having any ROM at all and they relied on external ROM. If I am right, you need to check the part number suffix to see what the chip capabilities really are.

author: grumpydoc
author_rank: Super Contributor
timestamp: December 19, 2012, 05:08:20 pm
content: You might be right but I can't see a ROMless version in the datasheet - certainly there are ROMless versions of the 68HC11.These are 68HC705B16's (and 1x 68HC705B16N), the datasheet says these have "EPROM" which would imply erasability, especially as there are versions with mask ROM described separately. They also separately talk about the EEPROM area that the chip has........Ah-ha, found it. When discussing the security bit there's a bit in the datasheet that says "To deactivate the secure bit, the EPROM has to be erased by exposure to a high density ultraviolet light" so these are presumably UVEPROM but with no window effectively making them one time programmable.The bin it is, then

author: SeanB
author_rank: Super Contributor
timestamp: December 19, 2012, 06:06:01 pm
content: Send them to Mike to toast on the output of the Xray scanner when he has it in burnin mode. 1 hour should blank them nicely.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 19, 2012, 11:20:06 pm
content: Quote from: SeanB on December 19, 2012, 06:06:01 pmNope. I've seen several discussions on this and the consensus was you'd need a level of x-ray that would damage the silicon before they got erased.I have a feeling that OTP HC11's can be used with external ROMs, although I may be confusing with a different ancient MCU

author: free_electron
author_rank: Super Contributor
timestamp: December 20, 2012, 12:20:09 am
content: Quote from: mikeselectricstuff on December 19, 2012, 11:20:06 pmdental x-ray machines will erase otp's ...

author: grumpydoc
author_rank: Super Contributor
timestamp: December 20, 2012, 09:30:13 am
content: QuoteIt's a pity I no longer have daily access to a linac. It would have been fun to find out what one could do.QuoteThe HC11s I picked up are all in a board with external ROMs - I think some of the variations shipped with the internal ROM "pre-disabled" and some have a control register bit that you can flip to take the ROM out of the memory map (plus possibly some external pins to tell the CPU whether the multi-function pins are I/O port or address/data.I just need to think of a project to make use of them now.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 20, 2012, 01:52:03 pm
content: Quote from: free_electron on December 20, 2012, 12:20:09 amDental units tend to have low duty cycles so probably wouldn't run long enough to do it.I'll give it a try - the beam on my baggage unit is probably too dispersed by the time it hits the tunnel, but I have a mailroom x-ray cabinet which would allow it to be close to teh tube.

author: grumpydoc
author_rank: Super Contributor
timestamp: December 30, 2012, 12:50:57 pm
content: I know that this is an old topic (and Mike's xray machine is no longer capable of xraying anything) but..QuoteI've just noticed that the Wikipedia page on EPROMS gives a figure of 500Gy (followed by annealing at 600oC), citing a May 1971 issue of Electronics Magazine as the reference (haven't followed that source up).That's, ahem, rather a lot of radiation - in humans whole body doses in a single exposure above 10Gy are invariably fatal even with medical support and doses at the 500Gy level would generally be expected to lead to death within 24-48 hours from massive CNS damage.I don't know what doses Mike's xray machine was capable of but if hereallystuck his arm in and got that image I'd expect it to be similar to diagnostic xrays - perhaps a bit higher as we're talking 140kV acceleration which is right at the top end of diagnostic stuff (the dose depends on beam current and time - I think Mike mentioned the current but not the time element). Anyway that would be a dose in the 0.01 to 0.1 milli-Sievert (1 Sv == 1Gy for the purposes of this discussion) range.Average background radiation is 2-3 mSv per year.I.e Mike's x-ray machine is probably about 5x106times too weedy to erase an EPROM.Gy - Gray - unit of absorbed dose. 1Gy = 1J/kg. 1Gy == 100radSv - Sievert - unit of biological effective dose. Sv equals Gy times a factor dependent on the irradiating particle. For x-ray photons the factor is 1.