57k6 char string onto a LCD with BS2sx?

jacksmith99

Hello,

Could I ask for some inspiration please?

I am trying to get a longer string (about 120 bytes), received with 56k7 baud, onto a LCD
but I am having trouble with the char RX routine.

I have got the basics working, such char output to LCD and char RX on much lower speeds (1200 and 2400).
Conclusion is a timing problem :-(

Tried different char capture routines:

* direct write onto the LCD, too slow - did not work, only garbled characters on LCD
* buffering RX'ed chars into scratch RAM then write to LCD, too slow - did not work, only garbled characters on LCD

Wonder if someone could share his/her wisdom, please?

Thanks,

Jack

Post Edited (jacksmith99) : 2/24/2007 9:29:18 AM GMT

Mike Green

The Stamps are really not going to be able to do this. They're just not fast enough and they can't listen to the receive line while they're doing anything else including setting up for the next group of characters to be received. If your transmission source can handle handshaking signals like CTS, you might be able to do this (there's an option on the SERIN statement for CTS ... have a look at the PBasic Manual). There are some 3rd party serial buffers (usually a specially programmed PIC processor) that can help. If you don't need to interpret or change the characters, you can switch the input directly to the LCD, but transmit your own information when the received source is quiet (put an or gate on the input of the LCD so either the Stamp or the received source goes to the LCD). Idle state on a serial line is usually a logic high (one) and the idle source will be ignored by the LCD.

jacksmith99

Hi Mike,

You have confirmed, what I thought, was the problem.

Unfortunately the RS232 sender device does not use handshake lines, but I like your idea of the serial buffer device.

Trawled the net but did not manage to find a small and simple enough solution, so will end up building my own,
probably PIC based little serial buffer.

Thanks for the tip!

Best regards,

Jack

Mike Green

Here's one example (search for "serial buffer") www.protean-logic.com/tickit/rsb509B_HTML_Cutsheet.htm

jacksmith99

Yap, found that one before.

This, unfortunately, is too small (RAM wise - need 128bytes minimum) and too slow (baud rate wise - need to receive 57k6 baud).

Thanks for your help!

Regards,

Jack

TechnoRobbo

http://www.ti.com/sc/docs/products/fifo/fifo.htm
SN74ACT2229
daisy chain a few

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Have Fun


TR

Mike Green

TechnoRobbo,
These are synchronous FIFOs. They require a clock and Jack needs to buffer an asynchronous unclocked data stream. He could add additional circuitry to derive a clock, but then he might as well add a UART plus a large enough parallel FIFO. At that point, he'd probably be better off to use either an SX48 or Propeller either of which can handle the data rates involved and the amount of storage needed.

TechnoRobbo

Sorry, here's TI UART with dual 64 byte buffer
http://focus.ti.com/docs/prod/folders/print/tl16c752b.html

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Have Fun


TR