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Describe RS232 signal

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Gregor Riepl 2022-08-13 20:43:52 +02:00
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README.md
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An ESP8266 expansion for the Commodore PET / CBM. An ESP8266 expansion for the Commodore PET / CBM.
## Description
Unlike the C64, the Commodore PET does not have a serial port. Unlike the C64, the Commodore PET does not have a serial port.
For that reason, most serial port adapters for the C64 don't work, and an For that reason, most serial port adapters for the C64 don't work, and an
alternate interface must be found. Furthermore, the user port on the PET alternate interface must be found. Furthermore, the user port on the PET
@ -33,9 +35,30 @@ The other pin mappings are as follows:
| Cassette Motor | CTS | PET->ESP | PIA1 CB2 | VIA PB4 | | Cassette Motor | CTS | PET->ESP | PIA1 CB2 | VIA PB4 |
| Cassette Sense | RTS | ESP->PET | PIA1 PA4 | PIA1 PA5 | | Cassette Sense | RTS | ESP->PET | PIA1 PA4 | PIA1 PA5 |
A suitable serial signal (RS-232-like) must be generated/decoded in A suitable serial signal (RS-232-like) must be generated/decoded in software.
software. Make sure that no cassette port #1 access is generated while Make sure that you don't access the cassette port #1 while the adapter is
the adapter is connected. connected.
For programming info, refer to this excellent document: For programming info, refer to this excellent document:
http://www.6502.org/users/andre/petindex/local/pet-io-2.txt http://www.6502.org/users/andre/petindex/local/pet-io-2.txt
## RS232 Waveform
| Logic | L | H |
|-------|-----|-----|
| CMOS | 0V | 3V |
| RS232 | +3V | -3V |
| Start | +3V | |
| End | | -3V |
_ ___ ___ ____
H | | | | | |
| | | | | |
L |_| |_| |___|
S 1 1 0 1 1 0 0 1 E
_ _ ___
+3 | | | | | |
| | | | | |
-3 _| |___| |___| |____
S 1 1 0 1 1 0 0 1 E