3 ms·

Well you could bit bang and the 9 bits wouldn't be an issue. (Even if you had a tiny PIC microcontroler just to do that) This is best solvable the closer to th

Well you could bit bang and the 9 bits wouldn't be an issue. (Even if you had a tiny PIC microcontroler just to do that) This is best solvable the closer to the device in question and in the simplest way possible.

ghoward 6y ago
Sorry, dumb question: what is bit banging?
- gspr 6y ago
  The practice of using software to literally toggle (or read) individual pins with the correct software-controlled timing in order to communicate with some hardware. To transmit a bit pattern 10010010 over a single pin channel, for example, you'd literally set the pin high, sleep for a some predetermined amount of time, set it low, sleep, set it low, sleep, set it high, etc.
- thristian 6y ago
  In order to exchange data over a serial connection, the ones and zeroes have to be sent with exact timing, so the receiver can reliably tell where one bit ends and the next begins. Because of this, the hardware that's doing the communication can't do anything else at the same time. And since the actual mechanics of the process are simple and straightforward, most computers with a serial connection have special serial-interface hardware (a Universal Asynchronous Receiver/Transmitter, or UART) to take care of it - the CPU gives the UART some data, then returns to more productive pursuits while the UART works away. But sometimes you can't use a UART: maybe you're working on a tiny embedded computer without one, or maybe you need to speak a weird 9-bit protocol a standard UART doesn't understand. In that case, you can make the CPU pump the serial line directly. It's inefficient (there's probably more interesting work the CPU could be doing) and it can be difficult to make the CPU pause for exactly the right amount of time (CPUs are normally designed to run as fast or as efficiently as possible, nothing in between), but it's possible and sometimes it's all you've got. That's bit-banging.
  - londons_explore 6y ago
    Consider being a teacher. Thats a good explanation.
stefan_ 6y ago
The irony is that while a tiny PIC can do bit banging easily, the mighty Pi will struggle with it.
- hazeii 6y ago
  I'm familiar with both, and have Pi's bit-banging at 8MHz. It's not hard-realtime like a PIC though (where I've bitbanged a resistor D2A hung off a dsPIC33 to 17.734475MHz). It's an improvement over the years, but surprisingly little since bit-banging 4MHz Z80's more than 4 decades ago, where resolution was 1 T state (250ns).
  - londons_explore 6y ago
    The 9 bit serial OP mentioned likely doesn't have a seperate clock line, so it is hard realtime and timing matters a lot, and I doubt the Pi could reliably do anything over 1 kHz baud with bit banging. You could do much better if you didn't run Linux.

ghoward 6y ago

Sorry, dumb question: what is bit banging?

gspr 6y ago
The practice of using software to literally toggle (or read) individual pins with the correct software-controlled timing in order to communicate with some hardware. To transmit a bit pattern 10010010 over a single pin channel, for example, you'd literally set the pin high, sleep for a some predetermined amount of time, set it low, sleep, set it low, sleep, set it high, etc.
thristian 6y ago
In order to exchange data over a serial connection, the ones and zeroes have to be sent with exact timing, so the receiver can reliably tell where one bit ends and the next begins. Because of this, the hardware that's doing the communication can't do anything else at the same time. And since the actual mechanics of the process are simple and straightforward, most computers with a serial connection have special serial-interface hardware (a Universal Asynchronous Receiver/Transmitter, or UART) to take care of it - the CPU gives the UART some data, then returns to more productive pursuits while the UART works away. But sometimes you can't use a UART: maybe you're working on a tiny embedded computer without one, or maybe you need to speak a weird 9-bit protocol a standard UART doesn't understand. In that case, you can make the CPU pump the serial line directly. It's inefficient (there's probably more interesting work the CPU could be doing) and it can be difficult to make the CPU pause for exactly the right amount of time (CPUs are normally designed to run as fast or as efficiently as possible, nothing in between), but it's possible and sometimes it's all you've got. That's bit-banging.
- londons_explore 6y ago
  Consider being a teacher. Thats a good explanation.

stefan_ 6y ago

The irony is that while a tiny PIC can do bit banging easily, the mighty Pi will struggle with it.

hazeii 6y ago
I'm familiar with both, and have Pi's bit-banging at 8MHz. It's not hard-realtime like a PIC though (where I've bitbanged a resistor D2A hung off a dsPIC33 to 17.734475MHz). It's an improvement over the years, but surprisingly little since bit-banging 4MHz Z80's more than 4 decades ago, where resolution was 1 T state (250ns).
- londons_explore 6y ago
  The 9 bit serial OP mentioned likely doesn't have a seperate clock line, so it is hard realtime and timing matters a lot, and I doubt the Pi could reliably do anything over 1 kHz baud with bit banging. You could do much better if you didn't run Linux.