----- Original Message ----- From: "Dave VanHorn" To: "Microcontroller discussion list - Public." ; "Microcontroller discussion list - Public." Sent: Friday, May 13, 2005 2:45 PM Subject: Re: [PIC] RS232, USART, and COM > > > > >I do understand now, i.e. RS232 is usefull to extend the u(s)art interface > >over a long distance, i.e. 1 or 2 or 3 meters, but when our signals travel > >only a few centimeters on a pcb, we do not need rs232 and in fact rs232 > >will simply be a hinderance. > > Exactly. Well, another difference (?) is also that RS232 has other signals apart from TX and RX which if I understand correctly belong to the UART, i.e. TX and RX come from the UART standard, the others (CTS,RTS,DSR....) are only RS232 signals, i.e. they do not exist in UART interfaces. > > I would also argue that async serial is a waste of resources at that level. > You can talk clocked serial over a couple of general I/O pins, > letting the slower device be the master. > This has many advantages. In async serial, you need to maintain > precise timing, and you need to process the char you've received > before the next one arrives. You can add handshaking pins, but it's > pretty much guaranteed that you will receive at least one more char > after you assert the handshake line to get the other guy to shut up. > > In clocked serial, the recipient toggles a clock line, and the sender > puts the data bits out when it sees the clock change. > So, the recipient can go off and do something that takes even several > seconds, and come back and resume the conversation right where it > was, even in the middle of a char. SPI is a hardware based version > of clocked serial, but some chips are not blessed with those internal > peripherals, and they have to "bit-bang" it, doing the protocol in > software as opposed to hardware. > > You can bit-bang async serial as well, but you have to keep those > timings accurate, and that can be pretty difficult without a timer, > and you may not want to use your timer for that. > > Engineering is the art of compromise. :) > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > No virus found in this incoming message. > Checked by AVG Anti-Virus. > Version: 7.0.308 / Virus Database: 266.11.9 - Release Date: 12/05/2005 > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist