Thank you, petey,

I’ve managed to set the time and date on my super-cheap DS3132 RTC (similar to DS1307 but more accurate) one byte at a time with i2cset:

insmod i2c-gpio-custom bus0=0,20,19

i2cdetect -y 0

i2cset -y 0 0x68 6 0x16 b

i2cset -y 0 0x68 5 0x02 b

i2cset -y 0 0x68 4 0x12 b

i2cset -y 0 0x68 2 0x11 b

i2cset -y 0 0x68 1 0x28 b

i2cdump -y -r 0-7 0 0x68 b

Theoretically, i2cset can write multiple bytes, but I haven’t gotten that to work yet. I’m now playing with the AT24C32 i2c eeprom on the module with the DS3132, since if I can get that to work, I can probably get an MCP23017 to work, and also a picaxe X2 microprocessor, which has memory which can appear on the i2c bus as a 128-byte eeprom.