Binary and hexadecimal address mismatch for PCAL6524

[sbah]

Hi,

I am running on an issue on the I2C bus addresses for the PCAL6524. The address in binary does not match the address in hexadecimal. i.e: 0100000 should give us 0x20 but it is saying 0x40 in the chip datasheet (p7/70). Can you guys clarify on what is going on?

[TomasVaverka · Accepted solution]

Hi,

The address in hexadecimal is actually the full 8-bit write slave address (R/W bit = 0).

PCAL6524 has fix value for A6 – A2 as “01000”, and programmable A1-A0 settings (depending on what is connected to ADDR pin).

If for example ADDR = VSS, then PCAL6524 uses 0x44 (“0100010” + “0”) for I2C write slave address, and 0x45 (“0100010” + “1”) for I2C read slave address.

If for example ADDR = VDD, then PCAL6524 uses 0x46 (“0100011” + “0”) for I2C write slave address, and 0x47 (“0100011” + “1”) for I2C read slave address.

BRs, Tomas

[sbah]

Hi Thomas, thank you for the clarification.

However, there is only one ADDR pin. It does give A1 and A0 bits different values depending on what is connected to it: SCL, SDA, GND and VS.

[TomasVaverka]

Hi,

Yes, A1 and A0 are not HW address pins, which is quite common in other devices, but 2 bits whose value depends on the connection of the ADDR pin as shown in Table 4.

BR, Tomas