Daryl's 6502 SBC help

[BigDumbDinosaur]

beholder wrote:

Ok! Got my first serial data sent back and forth between my computer and the SBC!!!!!
Hurray!

The bad news... it only works if I have my arduino providing the clock

If you want some help with this how about posting a schematic?

[beholder]

Sorry but I don't have a schematic

My SBC is a copy of Daryl's SBC 2.5 (http://sbc.rictor.org/info2.html) I tried to keep as close as possible.
I wire wrapped/soldered on a protoboard following his schematics.

The only differences from his schematics:
Not using max232, but an FTDI breakout board (https://www.sparkfun.com/products/9716)
Im only using RX & TX

EEPROM only
I have only 1 x 100uFarads electrolytic capacitor on the power supply.

I'll be posting pics soon
Thanks!

[Dr Jefyll]

beholder wrote:

Ok! Got my first serial data sent back and forth between my computer and the SBC!!!!!
Hurray!

I bet that feels good. Congrats!

Quote:

It's so bizarre, all I have to do is switch the oscillator with the arduino and it works! I can see in my terminal window the word "OK"
At least now I know is something to do with my 1MHz can oscillator.

Is it still the same oscillator with the TTL output? The 74HC541 you're using as a buffer actually isn't appropriate, as its inputs aren't rated to accept TTL levels -- just as the inputs on the 'C02 aren't rated to accept TTL levels. (It's more or less a fluke that the 74HC541 made any improvement. But it's not unusual to see bizarre stuff in circumstances like this.)

Do you have a 74HCT541 -- or some other 74HCT chip -- that you could use as the buffer? 74HCT chips do accept TTL levels at their inputs.

Alternatively, you could try adding a pullup resistor (say 2.2 or 3.3K) from the osc. output to VCC. Better yet, get rid of that darn oscillator and replace it with the proper part!

-- Jeff

[beholder]

Hi Jeff.
Indeed, it was very satisfying when I saw the words "OK" on my monitor

I only have the 74hc541, but I'll be ordering a new oscillator today from digikey!
Will try using a resistor, thanks for the tip!
Allmost there! Soon I'll have my own 6502 sbc
Thanks

[cbscpe]

If it is a problem with the TTL output level a pull up should show if this is the case. A TTL output can sink approx 16mA so if you add a 680-2200Ohm pull up to VCC to the output of your canned oszillator you should see if the level is the issue. The pull up will overwrite the high output level of the oszillator and bring the level at almost VCC level if you have only CMOS inputs connected to PHI2. At the low level the TTL output is strong enough to pull the output to approx 0.5V even with the load of the pull-up