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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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@ -2,6 +2,8 @@
An ESP8266 expansion for the Commodore PET / CBM.
## Description
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
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 Sense | RTS | ESP->PET | PIA1 PA4 | PIA1 PA5 |
A suitable serial signal (RS-232-like) must be generated/decoded in
software. Make sure that no cassette port #1 access is generated while
the adapter is connected.
A suitable serial signal (RS-232-like) must be generated/decoded in software.
Make sure that you don't access the cassette port #1 while the adapter is
connected.
For programming info, refer to this excellent document:
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