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retro 8088 project

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pb:
I'm working on a (what I thought would be) simple 8088 based retro thing.  The Fujitsu 8088-2 that came from digikey doesn't have a notch or single dot index on it.  Instead it seems to have a groove/index along one side of the chip.  Based on the orientation and similarities to the ceramic package version in the datasheet, I believe that the indexed side marks pins 1-20.  Is that the correct interpretation?  Unless I'm missing something, I can't find explicit confirmation in the datasheet.

The reason I am asking is that the circuit (based on the 8284/8088 circuit in Grossblatt's 8088 Project Book) is behaving oddly.  CLOCK and RESET out of the 8284 look correct but the address and control lines out of the 8088 don't seem to change from all zeros (not even tri-stated) after RESET goes back low.  There is some noise/bouncing on ALE and #RD when RESET first goes high but nothing after RESET returns low.  What I was expecting to see is the boot address and ALE to signal the initial instruction read.  I've tried measuring ALE using a scope and a LA.  Neither seemed to pick up any change in ALE (always zero).  There is no memory (RAM/ROM) connected yet so maybe my expectations are incorrect.  I'm running out of hw debugging skill.  Any help would be appreciated.

thanks...

pb:

no thoughts from the masses?

Feanor:
Likely no-one can find the specific data sheet you are looking at there are w hole lot of Intel ones out there all with appropriate notches. How about some links, pictures and screen shots?

slburris:
How are you connecting the -RST and -AEN1, -AEN2, RDY1, and RDY2 inputs to the 8284?
If they are unconnected, the processor could be held in reset or be waiting
eternally for a bus cycle to complete.

Look at the RESET and READY pins on the processor.  RESET show be low and READY should be
high.

You could also put a scope on the processor's clock input and make sure it looks
OK.  The old processors were pretty particular about voltage levels, i..e.
they weren't TTL compatible.  Hence the need for the clock generator chip.

Scott

pb:

--- Quote from: slburris on October 23, 2010, 02:27:25 pm ---How are you connecting the -RST and -AEN1, -AEN2, RDY1, and RDY2 inputs to the 8284?
If they are unconnected, the processor could be held in reset or be waiting
eternally for a bus cycle to complete.

Look at the RESET and READY pins on the processor.  RESET show be low and READY should be
high.

--- End quote ---

-RST is tied to an RC circuit with a diode set up such that -RST is held low for ~47ms.  This comes directly from the Grossblatt book.

-AEN1 and -AEN2 are tied to GND.  RDY1 and RDY2 were left unconnected.  This also is from the circuit in the Grossblatt book.  After looking at it more, it does seem odd that those are left unconnected.  I tied both high through pull up resistors and pulled -ASYNC high as well.  The problem remained though READY is now high.  :)


--- Quote from: slburris on October 23, 2010, 02:27:25 pm ---You could also put a scope on the processor's clock input and make sure it looks
OK.  The old processors were pretty particular about voltage levels, i..e.
they weren't TTL compatible.  Hence the need for the clock generator chip.

--- End quote ---

Looking closer at the clock, it does seem like it is out of spec but I'm not sure why.  Attached is a capture from the scope on CLK.  Vtop (4.26V) > Vch of the 8088 (3.9V).  Vbas (856mV) seems too high for Vcl (0.6V).  I'm not sure what controls the bias on the clock voltage though to bring it down.

I've followed the circuit from the book and have done a few experiments (removing the cap in series with the xtal, tying RDY1 & 2 high, etc...) without much luck.  The one place where I haven't followed the circuit was the substituting out two 510ohm resistors tying the xtal pins to ground.  I've tried 470 and 560 ohm varieties as I don't have 510's on hand.  

Another note/oddity... I'm using a source voltage of 4.7v from a bench supply.  If I try to bump that up to 4.9 the 8284 seems to 'shutdown' in that the outputs go to noise.  Not sure what that's all about either.

The datasheet for the mbl 8088-2: http://www.datasheetarchive.com/Scans/Scans-000/Scans-0012900.html
The datasheet for the p8284a: http://www.datasheetarchive.com/pdf-datasheets/Datasheets-32/DSA-636967.html


This whole exercise is to try and understand more about circuit building itself so any thoughts or debugging help would be appreciated.

[Updated] Added attachment with DaveCAD schematic.

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