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Johnfd
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Joined: 04/08/2023
Location: Australia
Posts: 9

Posted: 02:36am 13 Jul 2026

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I've not been able to find methods to save multiple variables onto FRAM. As a result I generated the code below.

Using ideas from contributors on the forum I was successful in saving a single variable. I was halfway there.

The code below relies on a Procedure (sub routine) to save each variable and a Function to recover the saved variables. It will work for a large number of variables.

Because I needed to save about 30 strings in the main program there was plenty of room in the MB85RC256 32 kByte FRAM. None of my strings are greater than 20 characters so I just used memory steps of 25 for a total save of <600 bytes. There's no point in saving space. If you really need to use up to 32kB, by knowing the size of each variable you could pass it in Mem%. Maybe this approach could be used if using only a tiny amount of FRAM like that in some RTC devices.

The save program passes the variable and the start memory location to a Procedure while the read function is passed the start of memory only. The read determines the end of a variable by looking for a return that was previously added to the string in the save routine.

Here's the code, you may want to remove all the comments if space in the PICO is an issue. In this test program I used different different variables for the output for checking only.

SETPIN 21,22,I2C 'set the pins for I2C
I2C open 100,100

Dim Entry1$ = "First" 'define and set some strings
Dim Entry2$ = "Second abcd12345"
Dim Entry3$ = "Thirty"
Dim Entry4$ = "Four"

Dim Out1$ as string 'these normally not used
Dim Out2$ as string 'as they would be same as saved vars
Dim Out3$ as string
Dim Out4$ as string
Dim InputV$ as string

'First save variables in start positions set by second param
SaveR(Entry1$,1)
SaveR(Entry2$,25)
SaveR(Entry3$,50)
SaveR(Entry4$,75)

'now read variables in start positions set by parameter
Out1$ = ReadV(1)
Print Out1$ 'Print statements for checking only
Out2$ = ReadV(25)
Print Out2$
Out3$ = ReadV(50)
Print Out3$
Out4$ = ReadV(75)
Print Out4$

Sub SaveR(InputV$,mem%) 'Save from memory location mem%
MSB=mem%\256:LSB=mem% Mod 256 'calculate 16 bit memory location
Temp$=Chr$(MSB) + Chr$(LSB) + InputV$ + Chr$(13) 'Address+string+CR
I2C write &B1010000,1,Len(Temp$),Temp$ 'Write address + string
End sub
'end of save procedure

'Start of read function
Function ReadV(mem%) as string 'read the variable and return the value
Str$ = ""
MSB=mem%\256:LSB=mem% Mod 256 'Change the 16 bit memory addresss into 2 bytes
I2C write &B1010000,1,2,MSB,LSB 'Set start address
Do
I2C read &B1010000,1,1,bVar% 'read one byte
if bVar%<>13 then Str$=Str$+Chr$(bVar%) 'if a return don't add to string
If bVar%=13 Then Exit Do 'if a return exit
Loop
ReadV = Str$ 'assign to the function output
End Function

End

Volhout
Guru

Joined: 05/03/2018
Location: Netherlands
Posts: 5978

Posted: 05:19am 13 Jul 2026

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Hi John,

Good work, Thanks for sharing.
The only thing I could improviseer, is making an index file. A file that container the (1,25,50,…)
Then you do not need to remember these Numbers.
That is especially interesting when there are variables with different size.

Volhout

PicomiteVGA PETSCII ROBOTS

PhenixRising
Guru

Joined: 07/11/2023
Location: United Kingdom
Posts: 1991

Posted: 11:23am 13 Jul 2026

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Great timing because I was just thinking about FRAM since I saw it on a grblHAL board.

Mikroe has a FRAM Click module

Oh, I see there are both SPI and I2C versions.
Edited 2026-07-13 21:26 by PhenixRising

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