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How to Start hardware of 8085up......??

Your 8085 is probably stuck in reset -- you should be pulling /RESET_IN to Vcc with the resistor, and grounding /RESET_IN to reset the processor. It's an inverted input, meaning it's active low. You should probably at least debounce the button to give a clean reset, and a Power-on-Reset/debounce combination would be better (you can build it with two NOT gates from a 74LS14).

Also, don't forget that the 8085 has several other lines that need to be pulled to various states for normal operation. You need to take care of the HOLD and READY lines, as well as the various interrupt lines.
 
Hi glitch,

The 8085 working in real is going over my head...
OK, I have connected reset_in to Gnd with Resistance 4.7K ( pull down) when i have to reset i just connect this pin to Vcc directly..
and the HOLD pin is open....
The crystal is 4MHz with 0.22 ceramic type at pin 2..
 
I must say that all 5 Trap, Rst , intr (interpt) are grounded and Ready is connected to Vcc.
 
RITESH said:
OK, I have connected reset_in to Gnd with Resistance 4.7K ( pull down) when i have to reset i just connect this pin to Vcc directly..
Click to expand...

You've got it backwards. Tie RESET_IN\ (I use the backslash to denote a negative logic pin) to Vcc through your 4.7K resistor. Ground it when you need to reset.

Similarly, tie READY to Vcc through a 4.7K resistor.
As mentioned, tie HOLD to ground.
And INTR to ground.
And TRAP to ground.
 
Tie RESET_IN\ (I use the backslash to denote a negative logic pin) to Vcc through your 4.7K resistor. Ground it when you need to reset.
Click to expand...

OK, i have done exactly like you say..is there any need of de-bounce switch there??

I have seen schematic where HOLD pin was open..

and please tell what to do of bypass capacitor across X1 and x2 i am not getting 22(22pf) i have 104, 222,etc like this ceramics capacitor.

I also find that the SOD is very slow that mean, when i start powers supply the led at SOD takes time to start and the time period is also not constant for some tomes it works for few secounds then change it time to more few seconds, on//off , exactly...
 
If you saw a schematic where HOLD was open, it was wrong. Leaving HOLD floating is an excellent way to ensure your project fuctions erratically.

Your crystal oscillator is probably having a hard time running, which is why you are seeing strange SOD change rates. If you're using a capacitor marked 222, that's a 2.2 nF capacitor, which is 2200 pF and won't work. The capacitor should also go from X2 to GND, not X1 to X2. You want a 15-30 pF capacitor, which will probably be marked with just two numbers and a letter (15J would indicate 15 pF with a tolerance code of J...the tolerance code doesn't matter for this application). I have a 47 pF capacitor from X2 (pin 3) to ground on both of my 8085 SBCs and they function perfectly, so the value really isn't critical.
 
If you need a small capacitor, try taking two insulated wires, each about 10 cm. long and twist them tightly together--but don't connect them together. Use each wire as the lead of the capacitor.

Back in the days of tube amplifiers, you'd do this to make small-value neutralizing capacitors. I haven't seen one in a computer circuit, but there's no reason why it shouldn't work.
 
Chuck(G) said:
Back in the days of tube amplifiers, you'd do this to make small-value neutralizing capacitors. I haven't seen one in a computer circuit, but there's no reason why it shouldn't work.
Click to expand...

Yep, this will work for 5-10 pF -- we called them "gimmick" capacitors. Never used one for a crystal oscillator, but we used them to neutralize parasitic oscillations through feedback in discrete audio op-amps. Start with about five twists and leave the ends of the leads long, then if you need more capacitance, you just add more twists.
 
Oh, heck, they got used for mixer injection, gas tube triggering...

Nothing like a couple pieces of wire.

If you've got some AWG 30 wire-wrap wire, the thin insulation and small wire size allows for some fairly good-sized capacitances in a small package.
 
OK, now i have connected 33pF capacitor to pin 2 of X2 and the 8085 SOd is not working well it takes time to start and glow continuously..
when i touch the crystal surface the LED off....
please tell what to do know??
 
OK, now i have connected 33pF capacitor to pin 2 of X2 and the 8085 SoD is not working well it takes time to start and glow continuously..
when i touch the crystal surface the LED off....
please tell what to do know??
 
What does your 33 pf capacitor look like? Based on your other capacitors, I suspect a misreading.

The simplest solution is just to run the 8085 from a packaged crystal oscillator. They're inexpensive and work.
 
No, its 33pf ( having black dot on upper side and the size is very small as you were showing...33 is written on it) ...
at that time when i supply on power the 8085 board, nothing happen( LED remain off).
on pressing reset switch the LED glow continuously....

after that, i just take out the PROM and read it's code that were totally diff. i don't know how does it happen..??
then i again programmed the EEPROM, the 8085 board LED at SOD was doing nothing.....



I want to ask more question which i notice with my buzzer, was that the all higher addr pin were pulsated at a time why???
If i am using 0000H to 1FFFH for PROM and 4000H to 5FFFH for RAM then, why the other addr pins were ruing from 3 to 8 decoder output..??
 
In my 8805 board the A15 to C A14 to B A14 to A..and 74138 G1 and G2 are connected to Vcc and Gnd as per data sheet....
So, the problem is that I am uin addr 0x0000H to 1FFFH for PROM and 0x4000H to 5FFFH for RAM..

The yo is connected to CE of ROM and y1 to RAM CE (i.e. low logic) ..
I found that the other Y1,Y3,Y4...giving outputs....( with the help of Buzzer connected across pin just for testing) I don't understand this why???
as you have sen my code before they are not using these addr.

One more problem, i found after this the code in PROM was automatically changed, i don't know how it happen??
 
0x4000 is a really crappy place to put your stack pointer. When you call delay it will try to push the return address to 0x3FFF and 0x3FFE. The DELAY routine will execute up to the return instruction then it will try to return to the address at 0x3FFF and 0x3FFE. Problem is that since there is no memory there the PC will be loaded with garbage and off you go into the weeds.

The stack pointer (SP) should be initialized to 0x5FFF for absolute safety. Sure this will waste a byte since the SP is decremented before any data is stored. After you get things working you can experiment.
__________________
Click to expand...

I got this from other people..
 
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