Hi All PICers !

Wednesday December 04 1996 11:12,
Ralf.Sigmund@STUD.UNI-HANNOVER.DE wrote in PICLIST:

 RS> I am about to start my first Pic Project. It is a small
 RS> device that should
 RS>
 RS>   (1) accept digital data (numbers & strings) from a
 RS> Measurement device via RS 232 at  any time.

You only receive data from this device ?  (1)

 RS>   (2A) store the Information in memory (approx. 20 Kilobytes
 RS> of data)

  It is the most problem. If you use 16C74 you can put one port as
DATA (8 bit), other ports as ADDRESS (15 bit for 32 kB)
and -CS,-WR,-OE (3 bit) : 8+15+3=26 bit. C74 have 33 bit I/O.
What about using 3x 6264 (8kx8 cmos static ram) or other with
more memory space (62256) ?  (I have many 6264 :-)
 13 bit for address, and 3 bit for chip selection.

 RS>   (2B) display the latest aquired data on a LCD display

If you want to built low-cost device try to use any 4-digit LCD
display with Microchip's AY-0438 controller. It require onle 3
wire (PIC's I/O) for communicate.

 RS>   (3) send all data to a PC via a second RS 232

Only send ?  (2)

 RS> After reading some FAQs there remain still some questions:
 RS>
 RS> What kind of Memory should I use (lithium battery backed up
 RS> static ram, EEPROM, Flash...)? How do I wire the memory to a
 RS> PIC? Any Circuits ?
 RS>
 RS> How do I wire two RS 232 ports ( one with Hardware Handshake
 RS> )?

 If (1) and (2) is true the best way is 16C74 that have serial port.

 RS> Do I need a UART or is just a simple MAX 232 signal
 RS> converter enough?

It's depend for the RS232 speed. If you not use high speed the
simplest (and low cost) solution is :
          +5v --------------| e
                    |      /
from PIC's TxD      R2   |/
    --->----- R1----|----|\  c
                         | \---------------------->---  RS232 RxD
                            |
                            |
                            R3         |\ |
                            |----------| /|-------<--- RS232  TxD
                           _|_         |/ |   |
                           ---+C1             |  R1,R2,R3 2-10 kOhm
                            |                 |  C1 5-100 uFx16-20v
                           _|_                |
to PIC's RxD                                  |
----------------<------------------------------

 I dont remember, mayby PIC's signals must be inverted.

Resume:
using 16C74 with 3x 6264 and AY-0438 :
  8data+13address+3xCS+OE+WE+2xRS232+3xAY =31 bit.
You have 2 I/O free for handshake.
---------------------------------------------------------------------
   Best Wishes, Alex Torres.
   Kharkov, Ukraine, exUSSR.
   E-Mail To : altor@cook.kharkov.ua   via InterNet
               or 2:461/28             via FidoNet

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