Caple C871i Manual de usuario descargar pdf (Pagina 39)

100

101

Apple II Computer Info

The Base of each transistor has a 1k or so Ohm resistor attached.

The resistor connected to each Base is the Input for that LED. This

should take care of driving the LEDs. When an Input goes Low (e.g. to

GND), the corresponding LED should light. If you feel brightness is too

high, increase the Base R value.

The rest of the circuit depends upon the conditions you choose for

lighting an LED and how many of what kinds of IC's you have in your

parts bin.

For example, you could use the condition: when /Enable is low and

/WR-REQ is low then /WR-LED is low. /WR-LED goes to the Write LED (Red)

Input. If /Enable is low and /WR-REQ is high then you assume a Read and

/RD-LED goes low to turn on the Read (Green) LED.

A single quad dual input NOR IC, like a 74LS02, could handle the

logic. In the circuit below, "[ ]" numbers are Disk ][ Analog board

connector points and "( )" numbers refer to pins on a 74LS02.

[10] /WR-REQ ------ (2)

NOR-1 (1)---- (5 & 6) NOR-2 (4)---- /WR-LED to

Red Input

[14] /Enable -------(3) |

_________________________|

|__________(11)

NOR-3 (13)--- (8 & 9) NOR-4 (10)--- /RD-LED to

Green Input

[14] /Enable -------(12)

(7) to GND

(14) to +5V

In the above, when /Enable is low, one of the LED's will light. If

/WR-REQ is low, the Red LED will light; if /WR-REQ is high, the Green

LED will light. (Some fiddling with resistor values may be required to

settle on the right ON brightness levels.) One advantage of this

circuit is that you always have a 'drive ON' indicator and, so, do not

need to drill a hole for another LED.

An alternative circuit could monitor actual Read [16] and Write

[18] activity using /Enable [14] to enable inputs to a dual 1-Shot IC.

Write transitions would fire the Write 1-Shot; Read transitions would

fire the Read 1-Shot. The /Q output from a 1-shot would connect to the

desired Red or Green Input. Pulse time for each 1-Shot could be

something like 1/5 second in order to guarantee a stable, bright

display.

Rubywand

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Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 39 of 572

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Caple C871i Manual de usuario Pagina 39

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Caple C871i Manual de usuario Pagina 39

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