Quote:
Originally Posted by dpeterson3
I need to write a serial protocol for it. I know it can be done, but I am not sure where to start. Any suggestions?
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Start by understanding the timing and bit arrangement of UART serial communications in general, then look at the specifics of your application.
The "idle" state of the data line is a logic 1, which is +5v in the case of TTL. A character begins with a logic 0 start bit, then continues with each of either seven or eight data bits in turn from least significant (the "1"s bit) to most significant (either the "64"s bit or "128"s bit), sometimes inserts an optional parity bit, then ends with either one or two logic 1 stop bits. So each eight-bit character uses either ten or eleven bits of time to send.
The way most serial receivers work, they will function with up to a 9 or 10 percent difference in clock rates between the transmitter and receiver. I assume the BitJet chip will listen at 9600 bps, with 8 data bits and one stop bit. That makes each bit just a little more than 100 microseconds long.
What language will you be using to program the Apple ][? Do you know how to do precise timing with it?