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8085 Project !!

M

Marty

Veteran Member
Joined
Jul 26, 2009
Messages
3,141
Location
Boulder , Colorado USA
Hi All;

Below is a picture of the start of my 8085 project..

All there is at present is Power and Ground connections..

I am using a 28C64, since that is the smallest of the Reprogramable EEproms that I have..
I will make it look like a 2708 for now, I can always go bigger..

Glitch, I may/could use some pointers from You..

The Software area, will be the real Stickler..

002.jpg

Here is the revised unit..

001.jpg

First Power-up..

002.jpg

THANK YOU Marty
 
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Hi All;

Because of it being too cramped, I went with a different medium, Wire-wrapped instead of Breadboard..
I am also making a change in the basic circuitry..
I am making a cross between the Old 8080 MMD-1 (BugBookVI) and the 8085 circuitry from the Blacksburg (Tycon) circuitry..

001.jpg

THANK YOU Marty
 
Hi All;

Christoffer, there is no software planning thing, as this is a Training 8085 CPU, to be used with BugBooks V and VI and 8080/8085 Software Design and 8085 Cookbook and Microcomputer Interfacing with the 8255..
Possibly the only software would be the use of Debug and TEA Tycon Editor/Assembler..

THANK YOU Marty
 
There were more than a few 8085 systems--and even more that used the CPU in embedded applications.

One great thing with the 8085 is that you could construct a working system with 3 chips. Limited, perhaps, but operational.

If some voice an objection that the 8085 has a relatively poor instruction set when compared with the Z80, there's always the NSC800, a Z80-instruction set CPU with what amounts to an 8085 bus.
 
The weirdest thing about the 8085 are the so called "serial IO" pins, which are not much more than simple IO pins, no shifting is done, all timing depends on the CPU :D
 
What's weird about them? Bit-bang is a time-honored way of doing serial comms. Even the AT-to-XT keyboard converter uses it. On the 8085, you get a free 1-bit I/O port as well as prioritized vectored interrupts--what other CPU of the time has that?
 
Hi All;

Remember, that I already have an S-100 8085 Spacebyte system, and that this one is a Learning system and nothing more..

I hope that remotely I might be able to figure out the Software thing, with this.. But, that is very remote.. Which is what this is for checking out both Hardware and mainly small Software routines that I can do and learn from..

Here is a latest Picture of what I think I will need to do my experiments with.. It is Not completely wired, not even barely started..

002.jpg

THANK YOU Marty
 
Hi All;

I think I have all of the Power and Ground that I need wired for now, later I will wire the 8155 and the Output Led's for it..
I have the first of the Led's wired from the 74LS75's for the three ports, when I get them all wired, and debugged, I will have a Picture..

001.jpg

THANK YOU Marty
 
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Not to rain on your parade but... Aren't those 'DigiTast' keyswitches mounted upside down ?
 
Hi All;

Gert, I don't know where I got them from, probably surplus.. I think I have about 20 of them..

I just used what I have here to make it work, nothing special about it..

THANK YOU Marty
 
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Hi All;

Xtech, It was surplus as well, from a company that is no longer in business..
But, I was asked this same question when I wired up the PDP 8i clone, and someone found a place to get them..
I don't Remember where, nor the size, but I think it was about 10 or 11 inches by about 17 or so inches.. I think they are about 30 to 40 dollars.. I am running out of spare Boards myself, as well as wire, so I will need to get some supplies soon..
Here is the Link ::
http://www.digikey.com/product-detail/en/169P84WE/V1011-ND/38869
I re-copied it, and now it seems to work..
I doesn't seem to work, the origional link is here, at posting #31..
http://www.vcfed.org/forum/showthread.php?49355-Build-your-own-PDP-8I-Part-3/page4

THANK YOU Marty
 
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Hi All;

I think I have it all or almost all wired..
But, the 74LS245, is getting Hot, So, I need to check all the wires to it and find what is Causing the problem..
Hopefully it's something Simple..

THANK YOU Marty
 
If the '245 is buffering the DATA bus (bidirectional), make sure you have the direction pin wired properly. If not, you'll have output to output half the time.
And of course, if one outputs a 0 and the other 1, you're shorting the chip internally.
 
Hi All;

What I have is pin 1, the Directional pin wired to the Rd (32) pin on the 8085, pins 2 thru 9 are wired to the 8085 Ad0-7 connections, and the upper pins of the 74LS245 are wired to the Rom and Ram and HP Display Leds..
Also, I am using a 74ALS245, is this too much for it to drive ??

THANK YOU Marty
 
That configuration should be right. Works in my 8085 system, atleast.
How many devices is it driving? -try ohming out its in/outputs and check if they're shorted to ground or VCC, that'll heat it up fast.
The processor is likely CMOS. ALS logic should be able to withstand a fanout of 20-40 devices, depending on TTL/CMOS.
You could always try adding some pullups on the non-CPU side to help it along.
 
Hi All;

Christoffer, Thanks for the reply..
"" How many devices is it driving? "" One Rom, 2716, one Ram 6264, and two hp numerical leds One upper, one lower four bits each..
And three upper and three lower data 7475's for the three ports.. I can pull these if need be..
"" You could always try adding some pullups on the non-CPU side to help it along. ""
Would that help with the heat problem ??

THANK YOU Marty
 
The 80C85 is CMOS; the standard 8085 is HMOS. Drive capability is 2 ma. nominal.

If this were my setup, I'd invert WR/ and use it to drive DIR on the 245. The reason is that in the absence of RD/ or WR/, the 245 is still driving the bus if RD/ is used. That may not be the best situation. The use of an inverter or two also provides buffering for the signal.
 
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