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8085 page

8085 page

 Project 1 Page 3
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The picture to the right shows all the power wiring done. It was at this point that I applied a PSU and found my dead short caused by the uncut track... After rectifying this error, the power pins to each of the ICís were checked to avoid any fried devices once  power is finally re-applied with the wiring completed and the ICís in place.

And another two hours later we have the picture below with the wiring complete....

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To the left you can see a picture of the project with itís power wiring done along with the decoupling capacitors and pull-up resistors. Mmm. Please ignore the THIRD resistor down in the group at the top left. Er.. it shouldnít have been there. Pins 26 and 27 on the 2764 EPROM need to go straight to +5V NOT via a pull-up resistor. The result? The oscilloscope revealed a permanently high data bus (like an blank EPROM would give)

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Some may notice though that there is something that is not meant to be there- in the form of the blue Ďblobí under IC6. This is in fact not on the basic project drawings, and is part of the SYSTEM CLOCK which goes to Pin 6 of the Z80 CPU.

As Iíve explained in other places on this site, the CLOCK applied to the CPU can vary in frequency; and on this occasion I happened to have a 1MHz ceramic resonator to hand (something thatís very similar to a crystal) so I used this. The Z80A in the socket would have worked with a 4MHz clock but in this circuit there is absolutely NOTHING to be gained in using it.

Fault Finding

Fault Finding

Data Sheets

Data Sheets

Another constructor may of course wish to use a 4Mhz,  a 2Mhz,  a 3.48Mhz, or even a complete oscillator module if one is to hand. Crystal oscillators can be made using many different circuits, comprising of logic gates or discrete components. In this instance I used one built around the three spare invertors in the 74LS14 IC6. Note that I have highlighted the FAMILY of  IC on this occasion. This is because the components of  MY oscillator were optimised for the LS variant of the 7414. If you use the HC, HCT, etc. the oscillator may not always start on power up, or may not run on frequency. In order to ensure that another family works with the circuit, alternative component values will almost certainly need to be selected.

EEprom Programmer

Programmer

Video Information

VIDEO info

Peripheral Circuitry

Peripheral circuitry

Central Heating and Z280's

Z280 and  Central Heating  Controllers

Concluding Ideas

Concluding ideas

Links

Links

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Well well! It actually worked when power was finally applied! (after curing the fault Iíve already mentioned.)  Note that the circuit also needs the RESET cap and diode mounted somewhere on the board. As you will see from the picture to the left, they are in the bottom RH corner alongside the blue ceramic resonator. It was about midnight when I took this and I was glad to see it finished!

The two pictures below show the extra oscillator components for anyone interested in using the circuit.

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As can be seen by the picture below, the simple ĎDigital Clockí program used to start off this project needs NO RAM! Iíve left the socket in to demonstrate other more interesting programs that need to use the stack, and require storage outside the CPUís own registers.

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http://www.hampshire-shops.co.uk

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