I²C RAM Bank

One kilobyte of Random Access Memory (RAM). This is volatile storage.

Addresses in the range [0, 1023] ([0x000, 0x3ff]) can be read and written by devices on the I²C bus. On start-up and when a USB Set Configuration command is sent, the memory will be set to the contents in the RAM Initialisation array. This in turn was specified by the RAM Initialisation Contents command on the USB’s I²C Interface. The default firmware sets the contents to all zeroes.

By default all addresses are writable, but an address mask can be configured via the Protected RAM Address Mask (Slave) command on the USB’s I²C Interface to change this.

Writes to protected addresses will result in a NACK. This behaviour allows, for example, an area of RAM to be reserved for the USB Host to write data into that I²C Masters can only read. The address mask does not alter the wrap-around behaviour of the address pointer nor the initialisation contents of the RAM. If a Master wishes to determine which addresses are read-only then it can query the Protected RAM Address Mask register in the I²C Interface Bank.