AT&T 6386 16 Mhz Speedup
Dennis S. Breckenridge
root at nebulus.UUCP
Thu Mar 16 03:28:37 AEST 1989
In article <48 at nisca.ircc.ohio-state.edu>, bobd at hpuxa.ircc.ohio-state.edu (Bob DeBula) writes:
>
> Last fall, I obtained an AT&T 6386 16 Mhz machine at a real reasonable (then)
> price. While I was installing my ESDI drive, I took time out to examine
> the upside-down motherboard. One peculiarity struck me immediately: the
> 386 chip is marked 20Mhz!!! Apparently AT&T (Olivetti) must have decided
> to standardize production. I also located the 32.000 Mhz clock chip (I
> think). Now the intriguing question is; Can I replace the clock chip (which
> appears to be soldered and I have no idea where to obtain the 40.000 Mhz
> equivalent) and get a 20 Mhz machine? My orignial memory which came with the
> machine was 80ns (overkill I think). I purchased 4 1Mb SIMMs from a chip
> peddler and installed them (and removed the 256K SIMMs which I promptly
> stuck in my MAC-II to make it a 2Mb machine). These SIMMs are 100ns (the
> chip peddler insisted that they work fine in a 20Mhz 6386). In any case,
> has anyone else noticed this (or done anything about it)? I think I'll
> hold off while the warranty lasts, but it seems awfully tempting to get
> a 20% or so increase in speed by replacing a clock crystal :-). Is there
> something I'm not thinking of (i.e. did Olivetti/AT&T put something in there
> to stop hardware hacks such as this?)? Thanks for any help you may give.
Not all 6386 Machines have 20Mhz Chipsets, in fact I believe you lucked out.
Comparing the 6386E the 6386 (20Mhz Desktop) and the 6386 (16mhz) I have found
that not only the crystal changes but several of the the PAL's. One PAL I am
sure changes is the PAL labeled PLYX or PLYS (depending on the run of the
machine) This PAL is documented as the CYCLEGEN PAL in the operations manual.
I have included a map of the 3 system cards with the PAL and PROM layouts.
The ongoing Saga of the 6386-6386E-6386(20Mhz) as defined by PAL layouts.
---------------------------
| CSL5 Tower/Desktop |
| CSL2 20 Mhz |
---------------------------
----------
| PLYP |
----------
------------------
Tower/Desktop | PBUQ (1.09) |
20 Mhz | PBVP (1.14) |
------------------
----------
| PLYR |
----------
------------------
Tower/Desktop | PBUZ (1.09) |
20 Mhz | PBVN (1.14) |
------------------
----------
| PLYV |
----------
----------
Tower/Desktop | PLYE |
20 Mhz | PLXX |
----------
---------- -----------
Tower/Desktop/20 Mhz | PLYG | | PLYT |
---------- -----------
---------- -----------
Desktop | PLYL | | PLYU |
Tower/20 Mhz | PLYX | | |
---------- -----------
---------- -----------
Desktop | PLYS | | PLY1 |
Tower | PLYZ | | PLY2 |
20 Mhz | PLX7 | | PLXH |
---------- -----------
---------- -----------
Tower/Desktop | PLY0 | | PLYK |
20 Mhz | PLXN | | PLXK |
---------- -----------
---------- -----------
Desktop | PLYH | | PLX2 |
Tower/20 mhz | PLYY | | |
---------- ----------- -------------------
| 80386 (16 Mhz) |
| or |
| 80386 (20 Mhz) |
| |
| |
-------------------
I have uncovered some anomolies when experimenting with the various
configurations. When the 20 Mhz System card is installed in the 6386E Tower
The system behaves normally but the reverse is not true. The 6386E System card
does not work at all in the 20 Mhz Desktop machine. When the CYCLEGEN 1.6 PAL
is inserted in the 6386E the System sporatically RESETS itself (not a UNIX
panic) but a hard reset. I summized that the CYCLGEN 1.6 is not a FAST device
and the BUS timming is too far out of spec and the machine just resets. Every
test I performed with the DESKTOP (20Mhz) machine performs flawlessly,
including running the Computone AT-8 Serial card (with Driver Version 4.27)
None of the BELL Technolgies cards work to my satisfaction (HUB-6, ACE and ICC)
in fact they all panic the machine when UNIX 3.2 is using the modem (ttymXX)
device. The Hard disk controller that is used in the Desktop (20Mhz) is a
WD-1007-WAH with several components removed, nameley the HARD DISK BIOS eprom
and the supporting logic. With the new SYSTEM BIOS (1.14) it now supports the
383Mb Hard disk under DOS as well as a new 81Mb Half Height ESDI CDC Drive.
The problems with the Desktop are but one, It comes standard with a 3.5 inch
floppy disk, DOS and UNIX come on 5.25 inch media. Even if we source a 5.25
inch drive the internal cable does not have the appropriate connector to match
the drive in drive position 0. The second drive can be a 5.25 inch but you
cannot boot the system from it.
Dennis S. Breckenridge
Integration Specialist
National Technical Support
AT&T Canada
==============================================================================
"A mind is a terrible thing to MAIL: Dennis S. Breckenridge
waste!" 206 Poyntz Ave
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UUCP: uunet!attcan!nebulus!dennis ICBM: 43 4 58 N / 87 55 52 W
50 megatons should do!
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