C2N232 pre-announcement

From: Marko Mäkelä (msmakela_at_cc.hut.fi)
Date: 2001-09-12 09:44:19

Yesterday evening I was able to correct the problems with the pulse
generator of my datassette emulator.  The first problem was
incompatibility between signal levels that I corrected by adding a 4k7
pull-up resistor to the "cassette read" signal.

The second problem was in the programming.  Even though I had read
somewhere that the signal polarity is significant, I thought that it is
nonsense, since the C64 only monitors high-to-low transitions on the
signal.  I was surprised when the VIC-20 finally recognized the pulse
stream, after I modified the firmware so that the cassette read line is at
low voltage level when inactive.  The only difference from the previous
firmware was the polarity inversion.

I could now upload the schematic diagram and the board layout to FUNET,
but I can't right now, since the server seems to be out of service.  Until
the documents are available there, interested parties can request the
files from me by e-mail.  The circuit board is simple; there are no jumper
wires.  Therefore I suggest that those who are interested in the device
build it themselves.

A summary of the features:

- few components: five capacitors, three resistors and two ICs,
  plus connectors
- standard RS-232 connection with hardware handshaking (CTS/RTS)
  (could be easily changed to software handhshaking (XON/XOFF))
- supports tape loading and saving
  (no feedback from the cassette motor signal)
- supports a custom transfer protocol similar to prlink
  (coming soon)
- could be used to interface a Commodore serial bus disk drive or
  printer emulator that runs on the other end of the RS-232 line
  (I'm not going to implement this)


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