working with external memory

malc-c · - 10th September 2010, 15:50

Hi,

I'm looking at using an external Eprom (something like an 24LC256) to store time and temperatures, which can then be downloaded to a PC application via the serial port. However I need some pointers from you guys.

I currently have a RTC chip from which I use just time information at present.

Code:

I2CRead SDApin,SCLpin,$D0,$00,[RTCSec,RTCMin,RTCHour,RTCWDay,RTCDay,RTCMonth,RTCYear,RTCCtrl]  ; read DS1307 chip

I then have the following routine to give me Hrs and Mins which I use in parts of the program where I need to compare the current time to pre-sets

Code:

timeH=(RTCHour>>4)                               'convert the BCD format of the hours register and store in variable timeH
timeH=(timeH &$03)*10
timeH=timeH+(RTCHour&$0F)

timeM=(RTCMin>>4)
timeM=(timeM &$07)*10
timeM=timeM+(RTCMin&$0F)                         'convert the BCD format of the mins register and store in variable timeM

Temperatures are read from a DS18B20 (4 off) and simply end up and an array variable - Temperatures[0] - [3], and are represented by a 3 digit decimal, so 234 would be 23.4C.

There should not be much change in the temperatures as this is for my thermostat project, so the logging interval doesn't need to be too frequent (as in realtime !) probably once per minute, maybe once every 5 min - depending on the amount of data I could store in the chip. So I guess I need to use something like

Code:

IC2write, address, timeH, timeM, temperatures[0], temperatures[1], temperatures[2], temperatures[3]

I would then have a "download data" button on the PC application which would send something like "D" to the RS232 port and then once detected jumps to a subroutine where it then reads the chips contents, sends them as a data stream back to the PC application, so a single data line would probably look like

Code:

1230300302297289

So sending that via serial

Code:

Hserout [dec TimeH, TimeM] 
Hserout [DEC3 Temperatures(0)]
Hserout [DEC3 Temperatures(1)]
Hserout [DEC3 Temperatures(2)]
Hserout [DEC3 Temperatures(3)]

This is where I get stumpped !

I would probably need to use some form of delimiting character to indicate the end of a data line, or could simply send a long data stream and let the software start a new line after every 16 digits. Either way I would need to loop the above in some way for each line of data. I would also would like the memory contents cleared after the "log file" has been downloaded, so would need suggestions on how to do that.

I would welcome your ideas, and if possible some sample code.

**aratti** · - 10th September 2010, 16:50

I don't think one byte is enough to store your temperature . with one byte the maximum reading will be 25.5 degree then 25.6 will make your byte overflow to 0.

Al.

malc-c · - 10th September 2010, 16:52

Sorry, should of mentioned, they are words

Code:

Temperatures      VAR WORD[4]
  Temp1           VAR Temperatures[0]
  Temp2           VAR Temperatures[1]
  Temp3           VAR Temperatures[2]
  Temp4           VAR Temperatures[3]

with bytes for time

Code:

	TimeH var byte     
	TimeM var Byte

malc-c · - 10th September 2010, 18:14

One alternative (assuming I can find it in the UK) is this

http://www.jianpingusa.com/datasheet...nstruction.pdf

Basically an SD/MMC card reader that communicates via serial

Ouch - $50