jbm@uncle.UUCP (John B. Milton) (01/21/89)
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@uncle.UUCP, n8emr!uncle!jbm@osu-cis.cis.ohio-state.edu (614) h:294-4823, w:764-2933; Got any good 74LS503 circuits?