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Signature analysis: Difference between revisions
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The idea is to describe "known good" states of signals in the system – typically when in some diagnostic / troubleshooting mode – as a four-digit "fingerprint" of that signal, when referenced to a known clock and defined start/stop conditions. The concept was introduced in [https://doc.xdevs.com/doc/HP_Agilent_Keysight/journals/1977-05.pdf Hewlett Packard Journal May 1977] along with their first SA instrument, the HP 5004A. | The idea is to describe "known good" states of signals in the system – typically when in some diagnostic / troubleshooting mode – as a four-digit "fingerprint" of that signal, when referenced to a known clock and defined start/stop conditions. The concept was introduced in [https://doc.xdevs.com/doc/HP_Agilent_Keysight/journals/1977-05.pdf Hewlett Packard Journal May 1977] along with their first SA instrument, the HP 5004A. | ||
The signature algorithm is a 16-bit [[wikipedia:cyclic redundancy check|cyclic redundancy check]] that can be efficiently implemented in hardware using a [[wikipedia:linear-feedback shift register]]. HP selected the polynomial x<sup>16</sup>+x<sup>12</sup>+x<sup>9</sup>+x<sup>7</sup>+1 instead of a standard CRC-16 or CCITT-16 polynomial, in order | The signature algorithm is a 16-bit [[wikipedia:cyclic redundancy check|cyclic redundancy check]] that can be efficiently implemented in hardware using a [[wikipedia:linear-feedback shift register|linear-feedback shift register]]. HP selected the polynomial x<sup>16</sup>+x<sup>12</sup>+x<sup>9</sup>+x<sup>7</sup>+1 instead of a standard CRC-16 or CCITT-16 polynomial, in order to ''scatter the missed errors as much as possible'' and to ''avoid selecting feedback taps that are evenly spaced or four or eight bits apart because the types of instruments [...] that we will most frequently be testing tend to repeat patterns at four and eight-bit intervals''. | ||
They also chose a particular "funny hex" format to display the resulting 16-bit number (four hexadecimal digits) to be read easily on seven-segment displays, as 0–9,A,C,F,H,P,U instead of 0–9,A,B,C,D,E,F. (Presumably, including "H" and "P" in the display was an extra benefit.) | They also chose a particular "funny hex" format to display the resulting 16-bit number (four hexadecimal digits) to be read easily on seven-segment displays, as 0–9,A,C,F,H,P,U instead of 0–9,A,B,C,D,E,F. (Presumably, including "H" and "P" in the display was an extra benefit.) | ||
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Signature analysis was only popular for a fairly short time in the late 1970s and early 1980s before increasing integration made it ineffective. | Signature analysis was only popular for a fairly short time in the late 1970s and early 1980s before increasing integration made it ineffective. | ||
Some arcade game manufacturers used signature analysis to allow component-level repair by field technicians. | Some arcade game manufacturers used signature analysis to allow component-level repair by field technicians. | ||
It is also possible to use signature analysis in a limited way in equipment that has not been designed for it, by inserting a "free run" or "NOP" adapter between the CPU and its socket. This adapter is wired to present a "no operation" opcode to the CPU, which then loops through all its addresses, generating specific and constant signatures on address lines, allowing these lines in the circuit to be tested or identified (see reference below). | |||
''to be expanded'' | ''to be expanded'' | ||
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[...] | [...] | ||
In 1978 Tek was developing | In 1978 Tek was developing a radically new analog/digital scope that had a microprocessor, A/D converter, digital memory, programming capability, and a GPIB interface (also originally developed by HP as the HPIB). All of this complex digital circuitry was going to make these scopes virtually impossible to be repaired in the Field Office Service Centers. | ||
[[Tom Rousseau]], the | [[Tom Rousseau]], the 7854 Project Manager, realized this was going to be a huge problem for the Service Centers. | ||
When Tom read the [https://doc.xdevs.com/doc/HP_Agilent_Keysight/journals/1977-05.pdf May 1977 Hewlett Packard Journal] which was entirely devoted to Signature Analysis, Tom realized this concept would make it much easier for the Service Centers to troubleshoot the 7854. | When Tom read the [https://doc.xdevs.com/doc/HP_Agilent_Keysight/journals/1977-05.pdf May 1977 Hewlett Packard Journal] which was entirely devoted to Signature Analysis, Tom realized this concept would make it much easier for the Service Centers to troubleshoot the 7854. | ||
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* [[SA501|Tektronix SA501]] | * [[SA501|Tektronix SA501]] | ||
* [https://devkits.handheldmuseum.com/Atari-CatBox/index.htm Atari CAT BOX arcade tester] / [http://gamearchive.askey.org/General/Test_Equipment/Atari/CatBox.pdf Schematics] | * [https://devkits.handheldmuseum.com/Atari-CatBox/index.htm Atari CAT BOX arcade tester] / [http://gamearchive.askey.org/General/Test_Equipment/Atari/CatBox.pdf Schematics] | ||
* [https://www.flippers.com/pdfs/KK-Signature2.pdf Kurz-Kasch Signature II] (1979) | |||
* [https://hc-ddr.hucki.net/wiki/doku.php/elektronik/signaturanalyse robotron 31020] (East Germany) | * [https://hc-ddr.hucki.net/wiki/doku.php/elektronik/signaturanalyse robotron 31020] (East Germany) | ||
* [https://www.eevblog.com/forum/testgear/signature-analyzer-project/ Signature analyzer project] @ EEVBlog Forum | * [https://www.eevblog.com/forum/testgear/signature-analyzer-project/ Signature analyzer project] @ EEVBlog Forum | ||
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==Links== | ==Links== | ||
* [https://hpmemoryproject.org/an/pdf/an_222.pdf HP Application Note 222 | * [https://hpmemoryproject.org/an/pdf/an_222.pdf HP Application Note 222, ''A Designer's Guide to Signature Analysis''] | ||
** [https://www.hpmemoryproject.org/an/pdf/an_222-1.pdf AN-222-1, ''Implementing Signature Analysis for Production Testing with the HP 3060A Board Test System''] | |||
** [https://www.hpmemoryproject.org/an/pdf/an_222-2.pdf AN-222-2, ''Application Articles on Signature Analysis''], 1979 | |||
** [https://www.hpmemoryproject.org/an/pdf/an_222-3.pdf AN-222-3, ''A Manager's Guide to Signature Analysis''], 1980 | |||
** [https://www.hpmemoryproject.org/an/pdf/an_222-4.pdf AN-222-4, ''Guidelines for Signature Analysis – Understanding the Signature Measurement''] | |||
** AN-222-5, ''Increasing Productivity in Manufacturing and Service with a Logic Troubleshooting System'', 1982 | |||
** [https://www.hpmemoryproject.org/an/pdf/an_222-6.pdf AN-222-6, ''Troubleshooting with Composite Signatures''], 1983 | |||
* [http://gamearchive.askey.org/General/Test_Equipment/HP/SigAnalNotes.pdf Troubleshooting Microprocessors with "Free Run" Fixtures] / [http://gamearchive.askey.org/Video_Games/Manufacturers/Atari/signatures/6502NOP.txt A 6502 NOP adapter] | |||
{{PatentLinks|Signature analysis}} | {{PatentLinks|Signature analysis}} | ||