National Semiconductor Mass Storage Handbook

Tony Duell ard at
Mon Jun 22 13:29:13 CDT 2009

> Hi Tony,
> Thanks Al for the heads-up on the datasheets !! Tony, do you think it is

Indeed. That was extremely fast and very helpful. At least I know what it 

> some kind of  Manchester / Miller encoder / decoder ? Do we know if it is a

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.

> National chip or has it's total identity been wiped ? Maybe Signetics or
> Plessey or TI or ?? Where are the power pins ( sometimes that is a good

A proverb about grandmothers and sucking eggs springs to mind :-) :-)

> tell ) ?   You mentioned 24 pin skinny DIP ? I'll keep looking. This is for
> some type of magnetic disk / floppy media system ?

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).

> Pinouts are the same for the AMD 8051 / 8053. Hope that helps.



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