38 lines
1.6 KiB
Markdown
38 lines
1.6 KiB
Markdown
# petwifi
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An ESP8266 expansion for the Commodore PET / CBM.
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Unlike the C64, the Commodore PET does not have a serial port.
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For that reason, most serial port adapters for the C64 don't work, and an
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alternate interface must be found. Furthermore, the user port on the PET
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doesn't supply any power, so an external power supply would be necessary.
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There is hope, however: The cassette port supplies 5V power and has
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suitable logic lines that can be used to emulate a serial port.
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The drawback is that serial communication must be fully emulated in
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software.
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Due to the different voltage levels of the ESP8266 and the PET,
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some voltage conversion is necessary. Luckily, this can be achieved with
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minimal circuitry: Converting from 5V to 3.3V can be done with a
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resistor divider. For the opposite direction, no conversion is
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necessary, because the voltage swing from 3.3V CMOS output drivers
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is sufficient to drive NMOS input gates.
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Special care must be taken for the MOTOR control line (which is used as
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CTS control input on the ESP): It is driven by a darlington array on
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a 9V supply rail.
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The other pin mappings are as follows:
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| PET pin | ESP pin | Direction | Internal connection |
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|----------------|---------|-----------|---------------------|
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| Cassette Write | RXD | PET->ESP | VIA PB3 |
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| Cassette Read | TXD | ESP->PET | PIA1 CA1 |
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| Cassette Motor | CTS | PET->ESP | PIA1 CB2 |
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| Cassette Sense | RTS | ESP->PET | PIA PA4 |
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A suitable serial signal (RS-232-like) must be generated/decoded in
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software. Make sure that no cassette port #1 access is generated while
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the adapter is connected.
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