How to read & write to a 25aa1024 (1 Mbit SPI Bus Serial EEPROM) via 16F88

**wolwil** · - 6th April 2010, 05:33

If you are still using the schematic from MeLabs then...

Nope I found that mistake of mine earlier and fixed it

The other thing I see in the data sheet is the last bit of the control byte sets Read or Write.
0 = READ
1 = WRITE

Yeah this one amazes me with PBP having an I2CREAD and a I2CWRITE command but yet you still have to tell it to READ or WRITE?!?!?!

Just to clarify I found this under section 5.0 saying that a READ operation should be a 1 and WRITE should be a 0

The last bit of the control byte defines the operation to
be performed. When set to a one, a read operation is
selected, and when set to a zero, a write operation is
selected.

PAUSE 10 'Is that long enough?

Yes I believe so because the 24FC1025 only has a 5ms delay needed

And you may have to add this but try the above stuff first
DEFINE I2C_SLOW 1

I tried it and got the same results, nothing but 255's.

Do you know if the 24FC1025 is flashed with all 0's or all 1's from the factory? Before I was getting %00000000 from var B1 and now I am getting %11111111 but I want to know if its actually reading that or if its a blip in the coding.

Here is the updated code:

Code:

DEFINE I2C_SLOW 1
SO      con     0                           ' Define serial output pin
T2400   con     0                           ' Define serial mode
contR    CON     %10100001                   ' Define Control byte
contW    CON     %10100000                   ' Define Control byte
addr    CON     %0000000000000111           ' 2 Byte Address of 7
D1      CON     %00000111
B0      VAR     BYTE                        ' Var for data being read
B1      VAR     BYTE                        ' Var for 2nd byte being read

b0 = 0
b1 = 0
I2CWRITE PORTB.1,PORTB.4,contW,addr,[D1]      ' Send the byte 1 to address 7

PAUSE 10                                    ' Wait 10ms for write to complete

I2CREAD PORTB.1,PORTB.4,contR,addr,[B1,B0]      ' Read address 7 into B1
                                               ' and address 8 into B0

Serout SO,T2400,["Addr",#addr,":",#B1," and then ",#B0,13,10] ' Print

I added a 2nd byte to check an address I have not written to and also get a 255 from that but early on in the code I set B1 and B0 to 0 and its getting changed somehow. So either I am reading all 1's from the addresses or the code is screwy.

PS sorry about the novel here, but its late and I tend to ramble when I'm tired.

Other notes:
I am using a 4MHz external clock to run the show if that matters. I will be switching to a 20MHz once I have everything working.

**mackrackit** · - 15th April 2010, 15:28

I picked up a couple of these 24FC1025 and I am not having any luck either.

A0 and A1 and WP are connected to VSS.
A2 connected to VDD.
10K pull up on SDA and SCL.
Tried "start/stop" sequence before and after I2C commands...

Out put to terminal is 0 no matter what.

Code:

'  18F6680  24FC1025
    DEFINE OSC 20
    @ __CONFIG    _CONFIG1H, _OSC_HS_1H
    @ __CONFIG    _CONFIG2H, _WDT_OFF_2H & _WDTPS_128_2H
    @ __CONFIG    _CONFIG4L, _LVP_OFF_4L
    
    TRISF = 0
    PORTF = 0
    DEFINE I2C_SLOW 1
    DEFINE I2C_SCLOUT 1
    DPIN    VAR PORTF.6    'I2C DATA PIN
    CPIN    VAR PORTF.7    'I2C CLOCK PIN
    CONTR   CON %10100001  'READ CONTROL
    CONTW   CON %10100000  'WRITE CONTROL
    ADDR    VAR WORD
    DATI    VAR BYTE
    DATO    VAR BYTE
    ADDR = %0000000000000000
    DATO = %11110000
    
    START:
    SEROUT2 PORTB.2, 16572,["TEST",$d,$a]
    PAUSE 1000
    
    HIGH CPIN:HIGH DPIN:LOW DPIN
    I2CWRITE DPIN,CPIN,CONTW,ADDR,[DATO]  
    HIGH CPIN:LOW DPIN:HIGH DPIN
    Pause 10                

    HIGH CPIN:HIGH DPIN:LOW DPIN
    I2CREAD DPIN,CPIN,CONTR,ADDR[DATI]        
    HIGH CPIN:LOW DPIN:HIGH DPIN

    Serout2 PORTB.2, 16572,["DATA IN ",BIN DATI]       
    SEROUT2 PORTB.2, 16572,[$d,$a]

    GOTO START

**mackrackit** · - 15th April 2010, 20:20

I give up...

**wolwil** · - 15th April 2010, 22:37

I give up...

Haha! Well at least I learned the problem isn't me

So does anyone out there know the assembly code to make this work???

**mackrackit** · - 15th April 2010, 22:39

When I get back tonight I am thinking of do some sort of bit banging, maybe that will work.

**Dave** · - 16th April 2010, 11:31

mackrackit, Why are you using 10 k's for the pullup's? I believe the spec. says 4.7K or lower.. Might be the problem....

Dave Purola,
N8NTA

**mackrackit** · - 16th April 2010, 11:49

The data sheet for this part call for 10k at 100 kHz and 2k for 400 kHz and 1 MHz.

It did not work at the higher speeds so I was trying it at the slow.