14 Jun
2004
14 Jun
'04
12:20 p.m.
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