Scanning wrote: sections 2 and 9 of the 1989 edition are up now under http://bitsavers.org/pdf/national/_dataBooks/1989_Mass_Storage_Handbook

That datasheet is on Datasheetarchive, so I'd got a pinout of that. The 8468 is similar in consept, but has more pins (I think it only came in a PLCC package) and thus a diferent pinout Thanks to Al Kossow, I've now seen all the datasheets (on bitsavers) and know that, alas, none of them apply to the chip I am looking at. The power and groudn pins don't agree, for example. All I can tell you is that it's some kind of data encoder/decoder. The Read and Write data signals, together with the Read and Write clock lines go directly to it. I've not traced out enough to know more. If you've got the data sheets to hamd, can you check if it's the same pinout as the 8051, please (it looks to be). -tony

Indeed. That was extremely fast and very helpful. At least I know what it isn't.. Yes. I think it's the circuit that combines and separates clocks and data pluses. Possibly RLL 2.7 code, I thought it might be a DP8463, but none of the signals match. A proverb about grandmothers and sucking eggs springs to mind :-) :-) OK, more seriously, I'll tell you what I've discovered. This is a chip on the logic board of an HP winchester drive with what I am pretty sure is an ESDI interface. This board has about 50 chips on it, inclduing the 8053 microcontorller and a custom PGA thing with 95 pins. The chip in question has a National Semiconductor logo and the HP house-code 1820-5422. It's a 24 pin skinnyDIP (normal 0.1" pin spacing, 0.3" between the rows). As I said, I think the host interface on this drive is ESDI. The read/write data and read/write clock differential signals from the 20 pin connecotr are buffered in the ovious way (I forget the numbers of the buffer chips, but I have data sheets on them) and then go to this device. I;'ve not traced many pins yet, but the ones I know are : 8 : +5V (Vcc) 9 : Master clock input (from a 20MHz oscillator can) 11 : Write Clock input 12 : Write Data input 15 : Read Data output 16 : Read Clock output 20 : Ground There are no other pins connected to power or ground, which pretty much makes the ones I've found the real power pins (as opposed to, say, mode control pins that are tied high or low). Thoes power pins are odd (not the corner pins). Thanks. -tony

Thanks... After reading the databook that Al kindly scnaned and put on Bitsavers, I came to the same conclusion. It's none of the obvious devices. I now know a little more about it -- it's the data encoder/decoder, and it may also do things like sector mark detection. Pin 4 is the encoded write data output, which goes to an external delay line. The taps on the delay line are selected by a '151 multiplexer, the control inputs on that come from pins 1-3 on this unknown IC. Presumably write precompensation. Output of the mux goes to the HDA connector. I wodner if it is a custom part... -tony

Do you happen to know the latest issue that had such a list in it? The list I have goes up to the mid-3000s (if you see what I mean), and I've seen higher numbers used on stnadard chips. -tony

Tony, My list agrees with Dave's in that there is a " hole " at 1820-5422. They list 5421 and 5423.... No date on my list but it goes up to 1820-8163. File is about 22 MBytes, so a little large to E-mail.... Best regards, Steven wrote: