Hi
I have been doing a bit of research about UK caller ID, and
As well as the line reversal there is an on hook tone alert signal sent before
the FSK signal to allow more reliable CID detection. full deatils from BT
website www.sinet.bt.com document number SIN 227
Would it be possible to recode the X100p to detect this tone to indicate the
begining of a caller ID sequence.
I believe this is the correct sequence of events
from reading this and from a reading a couple of caller id ic datasheets
- Polarity reversal occurs on the (idle) line.
- The exchange is silent for >= 100ms.
- The exchange puts an alert tone on the line for between 88ms and 110ms;
this tone consists of 2130Hz and 2750Hz (both +/- 1.1%); the receiver
should look for at least 20ms of both tones or 30ms of the lower tone.
- The exchange goes silent.
- Between 15ms and 25ms after the end of the alert tone, the receiver
should put a DC load and an AC load on the line. The AC load is described
as 827 ohms in series with {1386 ohms and 139nF in parallel}. The DC load
should be no more than 0.5mA (and should be well over the 0.12 limit for
an idle line). However, to clear the line of noise, the load should
a plain resistance of between 240 to 350 ohms for the first 14ms to
16ms of the DC load.
robb