MCP4231 vs. MCP4251?

[tumbleweed]

The way I read the datasheet it doesn't look like the first byte you're sending is correct (WriteOnPot0/WriteOnPot1).

The first 8-bits of the 16-bit command are: AD3 AD2 AD1 AD0 C1 C0 D9 D8
where D9 and D8 are the upper parts of the 10-bit wiper data, followed by the lower 8-bits of data D7-D0 in the second byte

The 7-bit part wiper settings are from 000H to 080H (full-scale), with 081H to 3ffH reserved
The 8-bit part wiper settings are from 000H to 100H (full-scale), with 101H to 3ffH reserved

I'm assuming you meant to use the binary constants

    WriteOnPot0 con %000001
    WriteOnPot1 con %010001

If so, you're always setting data bits D9 and D8 to '01' which means the wiper data is always from 100H to 1ffH


Try these instead

    WriteOnPot0 con %00000000
    WriteOnPot1 con %00010000

[keithv]

The way I read the datasheet it doesn't look like the first byte you're sending is correct (WriteOnPot0/WriteOnPot1).

The first 8-bits of the 16-bit command are: AD3 AD2 AD1 AD0 C1 C0 D9 D8
where D9 and D8 are the upper parts of the 10-bit wiper data, followed by the lower 8-bits of data D7-D0 in the second byte

The 7-bit part wiper settings are from 000H to 080H (full-scale), with 081H to 3ffH reserved
The 8-bit part wiper settings are from 000H to 100H (full-scale), with 101H to 3ffH reserved

I'm assuming you meant to use the binary constants

    WriteOnPot0 con %000001
    WriteOnPot1 con %010001

If so, you're always setting data bits D9 and D8 to '01' which means the wiper data is always from 100H to 1ffH


Try these instead

    WriteOnPot0 con %00000000
    WriteOnPot1 con %00010000

Thanks! That fixed it! I don't know why that previous code worked just fine for the 7-bit version, but it did. The 8 bit version didn't like it at all.