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)
Marko
Message was sent through the cbm-hackers mailing list
Archive generated by hypermail 2.1.1.