Am 29.09.2013 11:22, schrieb Vajk Fekete:
> The key piece of information is, that ds9490 uses the ds2490 chip. Which is
> kinda discontinued by dallas/maxim. At a point they stated they have made a
> huge lot that will last years, and stopped production. They may have
> restarted production, or are just keeping price high enough to fulfill the
> prediction "stock will last for years"
>
The assembled DS9490 adapter is a lock-in component for nearly all PC
cash registers, which use iButtons as a security token and this adaptor
for connecting them.
This is a small, simple cash-cow for Maxim, so I doubt it will ever
disappear. It is however hard to get the DS2490 chip from the usual
vendors to make own adaptors. You have to place an order >100 pieces to
get some.
> Your best bet is to get any clone that uses the ds2480 chip and some sort
> of usb serial port. As far as I know, the ds24080 is abou the same
> functionality as the ds2490, just missing the native usb interface.
>
They are quite different when scanning the bus for new chips. Both the
DS2480B and DS2940 have some acceleration function for making the
scanning faster and generating less interrupts. The DS2480B uses the
host's 16-Byte UART FIFO to scan for one onewire chip with one
interrupt, while the DS2490 (due to having more RAM and an own CPU) can
do that inpendendly of the host, relieving the CPU from the scanning
load even more.
Maybe it's time to make an own USB->Onewire adaptor with better search
acceleration than the FTDI+DS2480B types have. It could be based on a
cheap AVR µC and the Opensource V-USB firmware.
Kind regards
Jan
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