Miscellaneous Operating Systems/Hardware

it seems we can't reprogram DS1981U chips, they are read-only
I do not know the "1wire-standard", I am reading documentation from Maxim-IC
I'd like to emulated DS1981U chips by an external circuit (1 wire interface + CPLD)
in this case I will be able to have a reprogrammable device

has someone already tried that ?

1wire-overview (video)

ivelegacy wrote: it seems we can't reprogram DS1981U chips, they are read-only

Of course. That's the whole point of these chips. Some of them also have programmable memory, but there will always be some form of read-only memory used for device identification purposes.

ivelegacy wrote: I do not know the "1wire-standard"

This is basically I2C bit-banging, but over a single wire used to alternatively convey the clock and data signals. Adapting an existing I2C design to 1wire is almost straightforward, except for the device power supply (true 1wire devices have only, well, one wire, and must use some form of vampire capacity to feed off the signals it receives on the wire in order to keep state and be able to do the bit-banging correctly).

miod wrote: Of course. That's the whole point of these chips

yes, I can reprogram the serial EEPROM 93c256C and 24C256 (already done with success), but I can't reprogram DS1981U
they are both used to assign a MAC-address in our UNIX workstations (including a few SGI models)




based on i2c serial EEPROM 24C04, I have replaced with 24C512

this is my equipment, kindly provided by my university lab, and used for homeworks
these keys are obsolete, they were commonly used as credit to pay coffee cups
in my case we wanted to use these keys to read a passphrase over a magnetic interface
so, I built a copy of the key, and a copy of the magnetic reader/writer
and a copy of the hardware interface to manually read/write

the new generation goes under crypt engine, and we also got a study
how to make coffee key safer

from my reading 20 years ago when they were introduced, I think I remember that every iButton has a 128-bit serial number permanently burned in. there are many variations when you go beyond that, with eeproms, smartcard-like crypto, and even full Java interpreters but I don't know if the latter are still available.

robespierre wrote: I remember that every iButton has a 128-bit serial number permanently burned in

yes, so, as we can't reprogram these chips, my idea is to emulate them by a CPLD (or by a little MPU, AVR8 tiny ?)
I need to "adapt" the digital interface to 1wire.