rs232serial
I'm looking for a simple programmable device that has RS232 inputs and outputs that can take a string of ten numbers and output a modified string over 9800 9600 baud, 8 bits, 1 stop bit, parity: none.
For example:
input:
0123456789
output:
the+string+is+now+1234567890
I know I could do it with something like an Arduino but I am looking for something a little simpler and hopefully more reliable.
The ATmega series of microcontrollers (datasheet) has the ability to use 9 data bits without messing with the parity bit. This functionality is described in the timing diagram:
Note that the bits are numbered in the figure from 0-8, which is a total of 9 bits. The caption refers to this numbering, it does not indicate that you can use 0-8 data bits. The minimum number of bits in a character is 5, and the maximum is 9, not 0-8.
You can set the width of the data section by the UCSZ bits. The settings are described in table 19-7, pictured below:
To set this in C using AVR Libc, you would need to execute the code:
#include <avr/io.h> // _BV() macro, register definitions
// Set the Uart Character SiZe to 9 bits as described in table 19-7
UCSR1B |= _BV(UCSZ12 );
UCSR1C |= _BV(UCSZ11) | _BV(UCSZ10 );
Note that you'll probably want to specify the other bits in these registers while you're at it.
There are almost certainly other processors which support this feature set. Atmel's ATtiny processors have the same USART as the ATmega, and are code-compatible, their AVR32 processors have the same true 9-bit support, but a different programming interface, the dsPIC processors support it, but without a proper parity bit (see page 243 of this datasheet; set bits 1 and 2, PDSEL of the UxMODE register)...the list goes on. The first processor that I checked which did not support it was a Stellaris Cortex-M3 part, which supports 5-8 data bits, but not 8 bits.
In the end, though, you should do your processor selection based on other factors first. You wrote:
I strongly prefer SD card support, and Ethernet / Wifi would be nice (I don't care too much about BlueTooth or USB, so long as they don't significantly increase price).
Most people will access the SD card in SPI mode, and almost everything has an SPI port or two. Ethernet/WiFi is too generic a spec and a much harder requirement to meet - Do you want an integrated MAC with an MII interface? Integrated PHY? Would you prefer to do all the TCP/IP stuff on-chip, or offload practically everything to something like a WIZnet W5100 or Lantronix XPort. You can also use components like the Microchip ENC28J60 to move the MAC and PHY to an external chip, accessed over SPI. Your other requirements are much more exacting than a 9-bit UART.
In fact, you could probably use a $1.50 ATtiny as an SPI'/I2C<->9-bit UART converter if you wanted to. That would be much less expensive than choosing a sub-optimal processor for your other requirements.
Here is how I would suggest going about debugging this problem:-
Check the connections.. if you've mixed up signal ground and chassis ground (shield) you could get funny behavior just like you describe. Pin 7 on the DB-25 is the one you want to connect to DE-9 pin 5. I'll assume you're using a commercial adapter/cable or have one wired like this.
Maybe check the transmit out line to ensure it's idling at -12 ( < -3 anyway).
Make sure the instrument is set to RS-232, and not current loop (Jumper 7,8 and 1,2).
Try the most common serial port setting (9600/8-N-1), 9600 baud, NO parity, 1 stop bit switch 1, 2, 3 OFF switch 4, 5 ON switch 6 ON switch 7, 8 ON
Make SURE you understand which is 'OFF' and which is 'ON'. Don't laugh, I've seen this happen more than once, and some types of DIP switches are kind of ambiguously marked. If in doubt, an ohmmeter across the switch.. in fact you could check all of the switches to ensure they're working.
I like Realterm as a terminal program. It's free, and easy to change the parameters. Try it on something known working first of course, and look for an online tutorial. Really worth it.
If still gibberish after that, get a scope screen cap or photo and post it.
If you have a continuing need for a logic analyzer, this one is very cheap and relatively useful. Not as good as my Tektronix boat anchor, but this one will fit in a coat pocket. But I'd get a scope first if you don't have one. Even the worst scope is better than nothing.
Best Answer
You haven't stated how much computing is needed to transform the input to the output, but I'd use a simple, self-contained, 8-bit microcontroller, such as the Silican Labs C8051F305. Something like this will require very few external components, though you will need a logic-level-to-RS232 converter chip and a few misc. components, such as decoupling caps.
The micro above has 2KB of flash, 128 bytes of RAM, UART and does not require an external oscillator/crystal. It costs around US$2.00 in single quantities.