Well, I'm almost there...; HwNote12

[John B. Milton]

Hey all,

Well time for an update. I have finished laying out the board for the second
hard drive/P5.1 upgrade. I have also finished the definition for the PAL.
This is how it's gonna go (so far):

One PC board with 3 chips: 26LS31, 26LS32 and PAL22V10. The PAL incorporates
all the functionality of the "P5.1 Field upgrade PAL", that is, it will:

1. Latch and drive the 4th hard disk head select bit, HDSEL3*
2. Latch D4 when MCR2 is written to
3. Drive the latched MCR2 D4 onto the data bus when PHSTAT* is asserted.

Items 2 and 3 provide "revision level information", used to set revlev and
change your mother board from "P3...P5" to "P5.1". New functions provided by
the PAL22V10:

4. Latch DDRIVE1*, DDRIVE2*, DDRIVE3* so that four hard drives can be selected.
   Note that the bits for DDRIVE2* and DDRIVE3* are not defined in the include
   <sys/hardware.h>. I just picked the next two bits up from HDSEL3 and
   DDRIVE1*. They WOULD be defined thus:

#define	DDRIVE2	0x0004			/* Hard disk drive select bit 2 */
#define	DDRIVE3	0x0008			/* Hard disk drive select bit 3 */

5. Multiplexing of the hard disk data streams (all four)
6. An extra inverter, in case I need it later.

I will be using Gil's idea of getting signals from the existing P5.1 socket.
I know, "but what if I don't have the P5.1 installed?". No problem, you just
install the part of it my board will be using. My board needs additional
signals that are not on the P5.1 socket (you DID put a scoket in didn't you)

These are the signals from the old P5.1 socket used:
 2. PHSTAT*
 4. D4
 7. D0
 8. MCR2SEL*
 9. RST*
10. GND
17. HDSEL3 (not used, I drive it from my board)

The P5.1 socket has a number of unused pins, which I will be using:
 3. D3
 5. D2
 6. D1
13. GND (not connected on the UNIXpc side)
14. HDMUX (multiplexed hard disk data from the PAL)
15. GND (not connected on the UNIXpc side)
16. HDWRDAT (hard disk write data)
18. (left unused)
20. VCC

Yes, my board will be getting power from the P5.1 socket. The GND from the P5.1
socket is connected to the hard drive signal cable ground on my board.

Once the mother board modifications have been done to your machine, all you
have to do is hook up two cables: The hard disk signal cable (34 pin) and a
20 dip header to 20 pin dip head ribbon cable from the P5.1 to a similar
socket on my board. Since my board will not be permanently attached, if it goes
bad, all you have to do is unplug it. All three chips will be socketed, so if
one goes bad it should be easy to replace. This is the current parts list:

U1	PAL22V10	Pre-programmed PLD
U2	26LS31		Quad differential line driver
U2	26LS32		Quad differential line receiver
C1-3	0.1uf		Bypass, or decoupling capacitors
C4	50-100uf	Local surge supply.
R1-4	100 ohm		Line termination for 26LS32
JD1-4	20 pin header	For connection to four hard drives
JS1-2	34 pin header	One to the mother board, one to the external drives
JH1	20 pin socket	For connection to expanded host "P5.1" socket

Misc: 2-16 pin sockets, 1-24 pin socket, mounting hardware.

As I think I've already said, this board will work with or without the P5.1
already installed. If you have the P5.1 in, you've already got a lot of the
work done. If you don't have the P5.1 installed, or don't know what that is,
don't worry. As far as physical placement of drives goes, I have designed my
board to work best having ALL HARD DRIVES MOUNTED EXTERNALLY. Since there is
absolutely no way you can run a second hard drive inside, unless both drives
are super low power 3.5", I have assumed that since one drive HAS to go
outside, they should BOTH go outside. I have seen the UNIXpc sitting on a
regular IBM-PC clone box, and that should be the most cost effective solution,
since PC boxes and power supplies can be had very cheap. I have been told from
many different sources that the cables to the external hard drives can be as
long as THREE FEET, so you can have your hard drives sit in a corner and whine.

I have designed the board to fit in the left fan grate, since in my opinion,
it is the best place. Howevery, YOU DON'T HAVE TO if you don't want to.
Remeber, in the two drive configuration there will be no less than five cables
running to this board, three of which will be running outside the UNIXpc, just
begging to be tripped over.

I still have to check over my PC layout with some other people to make sure
what I designed can really be made. When I defined the PAL, I used a pretty
heafty SIMULATION section to test it out, so I don't expect problems there.
If anyone knows of a good, fast cheap (I know) PC board production company,
let me know. I'm going to be scrounging up the bucks to cover the setup fee
and a short run of boards. No, I don't need anymore Beta testers.

While I'm lining up a PC production facility, I'll be working on the
documentation and installation instructions. Right now I'm going to bed...

If you have any comments YOU BETTER TELL ME NOW!

John
-- 
John Bly Milton IV, jbm at uncle.UUCP, n8emr!uncle!jbm at osu-cis.cis.ohio-state.edu
(614) h:294-4823, w:764-2933;  Got any good 74LS503 circuits?