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STOP! Don't do anything as a result of post #300!

Fortunately, with the data bus being $F8 is a single-byte 6502 instruction SED (set D flag). This is just as good as a NOP instruction...

So, this is working.

Can you now scope the signals on CPU pins 26 through 33 looking for anything that is not a steady voltage (either HIGH or LOW).

Dave
 
daver2 said:
Unfortunately, that is not what I asked you to do back in post #291.

Let me write it out long-hand:

What I am talking of here by (e.g. UD8 pin 9 for D0) is the other end of the 1k resistor that is plugged into UD8 pin 9 be connected to the specified voltage source and not the UD8 pin 9 itself. Is this clear?

D0 (UD8 pin 9), D2 (UD8 pin 11) and D4 (UD8 pin 14) to 0V (UD8 pin 12).
D1 (UD8 pin 10), D3 (UD8 pin 13), D5 (UD8 pin 15), D6 (UD8 pin 16) and D7 (UD8 pin 17) to +5V (UD8 pin 24).

Dave
Click to expand...
OPS...sorry!
So must i connect UD8 pins 9,11 and 14 to pin 12 and
UD8 pins 10,13,15,16,17 to pin 24?
 
Why are you desperate? That is what we are expecting related to where you have wired the 1k resistors to.

It is clear that you are not following what we are doing. Let me explain.

The CPU reads instructions via the data bus. The data bus is wired to the ROMs (amongst other things).

We have hard-wired (via the 1k resistors) the eight lines of the data bus to a fixed voltage. I was asking you to wire the resistors so that we get a NOP instruction ($EA) but you wired the resistors so that we get a SED instruction ($F8).

Both of these instructions are single byte instructions that do not perform any data bus reads or writes - so the only activity we should see on the data bus are the voltages we have set-up via the resistors.

Basically, the 6502 CPU is executing the same instruction over and over and over and over, ..., over and over and over, ... again - until you turn the power off. This is a NOP generator made out of resistors on the data bus, instead of being on a 'socket sandwich' that we insert between the CPU and the CPU socket. And, rather than using a NOP instruction - we are (accidentally) using a SED instruction.

What I want to know is does there appear to be any noise on the oscilloscope signals you are reading. Can you post a video of pins 29 and 30 and I will have a look for myself.

Dave
 
daver2 said:
Why are you desperate? That is what we are expecting related to where you have wired the 1k resistors to.

It is clear that you are not following what we are doing. Let me explain.

The CPU reads instructions via the data bus. The data bus is wired to the ROMs (amongst other things).

We have hard-wired (via the 1k resistors) the eight lines of the data bus to a fixed voltage. I was asking you to wire the resistors so that we get a NOP instruction ($EA) but you wired the resistors so that we get a SED instruction ($F8).

Both of these instructions are single byte instructions that do not perform any data bus reads or writes - so the only activity we should see on the data bus are the voltages we have set-up via the resistors.

Basically, the 6502 CPU is executing the same instruction over and over and over and over, ..., over and over and over, ... again - until you turn the power off. This is a NOP generator made out of resistors on the data bus, instead of being on a 'socket sandwich' that we insert between the CPU and the CPU socket. And, rather than using a NOP instruction - we are (accidentally) using a SED instruction.

What I want to know is does there appear to be any noise on the oscilloscope signals you are reading. Can you post a video of pins 29 and 30 and I will have a look for myself.

Dave
Click to expand...
Ok now i understand....i see clean signals without noise on these...
 
Excellent.

My mistake, I meant pins 30 and 31.

What I would now suggest is to change the voltage that our eight 1k resistors are wired to to give us a different 6502 instruction pattern ($AA = TAX).

Disconnect the ends of the resistors that are plugged into UD8 pins 12 and 24. There should be eight in total.

Connect the free ends of the 1k resistors as follows:

The free end of the resistor that is connected to UD8 pin 9 (D0) needs to be connected to 0V (UD8 pin 12).
The free end of the resistor that is connected to UD8 pin 10 (D1) needs to be connected to +5V (UD8 pin 24).
The free end of the resistor that is connected to UD8 pin 11 (D2) needs to be connected to 0V (UD8 pin 12).
The free end of the resistor that is connected to UD8 pin 13 (D3) needs to be connected to +5V (UD8 pin 24).
The free end of the resistor that is connected to UD8 pin 14 (D4) needs to be connected to 0V (UD8 pin 12).
The free end of the resistor that is connected to UD8 pin 15 (D5) needs to be connected to +5V (UD8 pin 24).
The free end of the resistor that is connected to UD8 pin 16 (D6) needs to be connected to 0V (UD8 pin 12).
The free end of the resistor that is connected to UD8 pin 17 (D7) needs to be connected to +5V (UD8 pin 24).

Check the CPU pins 7 (SYNC) and pins 26 through 33 again. You should observe pin 7 pulsing and different fixed voltages on pins 26 through 33. Report the logic levels.

Scope the data lines and ensure you get nice fixed dc voltages without noise.

Dave
 
daver2 said:
Excellent.

Next, have a look at the oscilloscope traces...

Dave
Click to expand...
Very clean traces :( I am desperate!!!
Maybe 2716 eprom for pettester isn't compatible with this pet??? Time to doubly 2k bin file and after insert on 4k eprom ???
 
You are not desperate, we are working the problem through logically. Each test tells us something and should either rule out a potential issue or lead us in the direction of the problem.

That is also what I am thinking at this stage.

However, before we get there, I would like you to use your oscilloscope on the following pins please:

UD9 pins 8, 7, 6, 5, 4, 3, 2, 1, and pins 23, 22, 19 and 18 in this order please. Please report back their frequency and ensure they are nice 'clean' signals that switch between 0V and approximately +5V.

Can you also check UD8 pin 20 for activity. You should observe a narrow low-going pulse. Can you report the frequency of this signal and ensure it is also a nice 'clean' signal that switches between 0V and approximately +5V.

Dave
 
I know that. I am not expecting a ROM to be in the socket. We are using the socket as a convenient point close to the ROMs to check the address bus.

If you can't stick the oscilloscope probe into the socket to make contact with the pins, attach a short piece of solid core wire to the end of your oscilloscope probe and use that.

Dave
 
daver2 said:
UD9 pins 8, 7, 6, 5, 4, 3, 2, 1, and pins 23, 22, 19 and 18 in this order please. Please report back their frequency and ensure they are nice 'clean' signals that switch between 0V and approximately +5V.
Click to expand...
UD9

8= 250 KHZ
7: 125 KHZ
6: 62,5 KHZ
5: 31,2 KHZ
4: 15,6 KHZ
3: 7,8 KHZ
2: 3,9 KHZ
1: 1,9 KHZ

23: 0.976 KHZ
22: 1,2 KHZ but i can t see a waveform....only a flat signal
19: 14,3 KHZ but flat signal
18: 0,12 KHZ
 
Pins 8 through 1 are fine.

Pins 23, 22, 19 and 18 not. Pin 23 may be OK though.

Are you adjusting the oscilloscope timebase to get a couple of cycles of the waveform on the screen or not? You should be...

If you can't see the waveform on the screen - don't rely on the frequency indication.

Think about it... If the oscilloscope is indicating a frequency, you should be able to see it!

Dave
 
daver2 said:
Pins 8 through 1 are fine.

Pins 23, 22, 19 and 18 not. Pin 23 may be OK though.

Are you adjusting the oscilloscope timebase to get a couple of cycles of the waveform on the screen or not? You should be...

If you can't see the waveform on the screen - don't rely on the frequency indication.

Think about it... If the oscilloscope is indicating a frequency, you should be able to see it!

Dave
Click to expand...
Good morning Dave,
i tried to adjust timebase setting and trigger but i can't see any waveform signal :(
 
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