National Semiconductor Mass Storage Handbook

Indeed. That was extremely fast and very helpful. At least I know what it isn't.. > some kind of Manchester / Miller encoder / decoder ? Do we know if it

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 :-) :-) > tell ) ? You mentioned 24 pin skinny DIP ? I'll keep looking. This is

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