What is this??? - Update

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon Jun 14 19:20:40 2004

>
> Hi again,
>
> I just opened it up....
> It's got 5 chips inside it.
> 74LS00
> 74LS74
> 8251AP-5
> 74LS32
> 4060
>
> Does this help??

YEs, a lot... Assuming there aren't significant numbers of transistors
around (to implement RS232 buffers in discrete components), then this
thing would appear to use TTL levels for the interface.

The 8251 is a serial chip (actually a USART, but I doubt it's eve used in
synchronous mode). It doesn't have an internal baud rate generator.

The 4060 is a long CMOS counter. My guess is that this produces the baud
rate clock, and in the absensce of any other chips, it's going to be
fixed at 1200/75 (there's no output port/mux chips there to allow for
selectable baud rates, and not really enough logic to implement that
using gates and FFs).

>
> I know that prestel is some sort of teletext service - and perhaps a
> dial-up service, but this unit doesn't really look like it's related to
> a modem.....

It is a seiral interface, presumanly for a special modem.

-tony
Received on Mon Jun 14 2004 - 19:20:40 BST