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Pulses on breadboard supply lines

I have been put together a circuit on solderless breadboard that links a z80 to my pc serial port. I ran a program that continually sends data from the pc and the z80 circuit echoes it back so I can see that it works ok. The problem is that characters being sent are sometimes being corrupted. If I put my logic probe on the ground lines off the breadboard, a pulse on the ground line is heard at the same time a character is corrupted. I'm assuming it's these pulses on the ground lines that are causing a mis-read of data. The data is only being read and transmitted at 9600bps.

How can I get rid of these glitches?

Reply to
bonzer
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Is the Z80 supply bypassed with a capacitor very close to the processor? What other chips are involved in this circuit? What is the source of power?

Reply to
John Popelish

The z80 does have a capacitor across the line near it. There are two breadboards that are linked. The first has the Z80, an eprom, some ram and a few logic ic's and the second board has a Zilog SIO/0, a CTC and max232 ic on it. The source of the power to both boards is a PC ATX power supply (5v).

Reply to
bonzer

Idunno, put on more caps? LOL

Electrolytics with low ESR, like removed from switching supplies, might help. Not that contact resistance helps that any, but that shouldn't matter too much. (I've pulled 20A through them protoboard rails and it seems okay with it!)

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

John, the supply is clean most of the time EXCEPT when there's a LOT of switching activity - ie, transferring lots of data on the serial line. I will try to get some pics of the board(s).

Reply to
bonzer

Is the supply clean if you load it with just a resistor that draws the same average current as your circuit?

A picture or three of your assembly might be helpful. Do you have place on the web to post a few? Do you have an ISP that allows you to post pictures through the newsgroup,

alt.binaries.schematics.electronic

Reply to
John Popelish

A picture of the scope trace that shows the supply pulse might help, also.

Reply to
John Popelish

Use a PCB !!

Signals over 100Khz is to high for a solderless breadboard.

Donald

Reply to
Donald

For something like this on protoboard, I've been known to use three or four bypass capacitors on one processor. Like a 1 uF tant. in parallel with a .1 ceramic from Vcc to Gnd, and another .1 ceramic from each power pin to the opposite bus. And the buses themselves usually get at least 3, preferably about 5 or 6 of different values.

I'm sure this will start flames, but I don't believe it's possible for there to be too many bypass capacitors.

I don't think I'd try to do anything faster than a typical Z80 on a protoboard, however.

Good Luck! Rich

Reply to
Rich Grise

Idunno, I've ran PWM on the order of 25-50W on mine at that frequency. ;-)

At higher RF, signals tend not to stay in the wires anyway so I don't mess with it to begin with ;-)

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

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