Re: Track/Sector Indicator on Drives

From: Marko Mäkelä (
Date: 2003-09-24 13:35:11

On Wed, Sep 24, 2003 at 03:35:53PM +0800, wrote:
> One thing I didn't uderstand from the schematic (not being able to read
> german) is how are the LEDs refreshed... is the memory location accessed
> often enough that the display is updated and steadily lit?

The address lines of the 2764 EPROM are fed by the data lines of the 6502 bus.
It looks like the comparators in t&s-display3.jpg, the figure with the
caption "Der Schaltplan des Moduls" generate a latching signal for the
BCD-to-7segment decoders.  In other words, the outputs of the EPROM are
changing all the time, and only when the address matches with the ones set
with the jumpers, one pair of the four 7-segment display drivers latches
the inputs.

Page 1 of the article mentions that the LCD display (as opposed to the LED
display) needs a 30 Hz to 100 Hz frequency on pin 1.  It looks like this
frequency is generated with the capacitor-and-resistor-and-inverter circuit
on the right side of the EPROM.


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