User's Manual

RPT 633
TM1184 Issue 1 Page 3 - 9
Switching from Speech to Data
29. The speech cancel signal consists of 1.25s of binary 1s. In the speech mode IC1-7
is high with the result that IC2-1 is low. The negative-going leading edge of the first
bit of data clocks IC1a so that IC1-7 goes low, switching PL1-3 to the low DATA
mode. The negative-going transition at IC1-5, IC1a times out with the result that:
a) IC1-7 goes high putting PL1-3 into the quiescent condition.
b) IC1-6 clocks IC1b for 2ms.
c) The combined lows at PL1-4 and IC1-6 result in IC2-4 going high.
30. As IC1-10 goes low again, after 2ms, it clocks IC2 with the result that IC2-3 goes
low, IC3-4 goes high and PL1-2 returns to its quiescent high condition.
Figure 5: Switching Into Speech