Page Comparison

The decoder chip above works. It replaces 1/4 of the 74139 for the Z88 design.

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Part No	Chip	Manufacture	Speed nS			Package	Price
			Min	Typ	Max
1741279	SN74LVC2G32QDCURQ1	Ti			<2.5	SM8	$ 0.55
	SN74LVC1G139DCUT	Ti / Farnell			<2.5	VSSOP	£0.404

The 2 -to-4 Line Decoder display input positive display or gates fast times.

Here is the chip that has been chosen:-

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Logic Lab Test v Truth Table

The decoder logic was and OR gates were checked against the Simplified Schematic with thanks to http://www.neuroproductions.be/logic-lab/ for the simulator.

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Updated 17/11/2016To be Updated wrong circuit displayed

View file

name	20161117c Turbo Decoder - Z88 Card.pdf
page	Turbocharging the decode chip
height	250

All the components required cannot be are fitted on a single card. The design has been split onto two cards. The first PCB is just for the Z88.

If a full 74139 74xx139 chip is required another PCB with the extra components it can be either be

piggy backed (using the DIL connections) to this Z88 Turbo card if the 16 Pin SOIC footprint is required or
used on its own with pins, plugged into a 16 pin DIL socket on the board where the original 74xx139 was..

	Photo	Dia hole mm
8 way header	Image Added	1.00	http://uk.farnell.com/te-connectivity-amp/826629-8/header-1row-8way/dp/3418364	£0.596
	Image Added	0.90	http://uk.farnell.com/te-connectivity-amp/215297-8/socket-vertical-1row-8way/dp/3419101	£0.54

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Note

title	Signals not the same abbreviations as the circuit

The names of the signals on the scope are not all the same as shown in the circuit.

Small holes are drilled in the centre of the pads of H1,so that wire links may be used to connect the signals from the 512K/512K card to the PCB.
The pads of the footprint of the SOT-23-5 have been made longer, to enable easier soldering of the small parts.
The bottom Left Hand corner of the PCB matches the shape of the 512K/512K Card for easy alignment.

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